UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL   SCIENCES 

Vol.  1,  No.  10,  pp.  291-339  April  29,  1916 


FUNDAMENTAL  INTERRELATIONSHIPS 

BETWEEN    CERTAIN    SOLUBLE 

SALTS  AND  SOIL  COLLOIDS 


BY 

L.  T.  SHARP 


INTRODUCTION 

"While  engaged  in  an  extensive  investigation  of  the  physio- 
logical effects  of  NaCl,  Na2S04  and  Na2C03  on  crop  plants  as 
grown  in  the  Davis  clay  loam,  in  cylinders,  under  field  condi- 
tions, the  writer  observed  that  the  soil  to  which  the  salts  had 
been  previously  applied  became  so  impervious  during  the  course 
of  the  experiment  as  to  retard  markedly  the  rate  of  percolation. 
So  pronounced  was  this  effect  that  during  the  winter  and  early 
spring  months  all  of  the  salt-treated  soils  were  continuously 
covered  with  standing  water.  The  appearance  of  this  striking 
modification  in  the  permeability  of  the  soil  to  water  in  the  salt- 
treated  soils,  together  with  the  inferior  cultivating  qualities 
exhibited  by  them,  impressed  us  as  evidence  of  the  fact  that  the 
salt  treatments  under  the  field  conditions  of  the  experiment  had 
effected  a  fundamental  change  in  the  physical  constitution  of  the 
soil.  The  occurrence  and  nature  of  this  change  and  its  relation 
to  soil  colloids,  interior  surface,  and  other  properties  of  soils, 
form  the  considerations  with  which  this  paper  is  chiefly  con- 
cerned. 

Just  such  an  effect  on  the  physical  condition  of  the  soil  as 
described  above  had  been  anticipated  as  the  normal  result  of 
adding  Na2C03  to  the  soil,  for  this  salt  has  generally  been  con- 
ceded, by  soil  experts,  to  be  an  active  deflocculating  agent.     But 


292         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

to  find,  on  the  other  hand,  that  a  similar  state  of  diffusion  existed 
in  the  soils  to  which  NaCl  or  Na2S04  had  been  added  appeared 
wholly  inexplicable  in  the  light  of  the  prevailing  conception  of 
these  salts  as  agents  capable  of  producing  flocculation  in  the 
soil  colloids.  However,  this  apparent  contradiction  of  well- 
established  facts  brought  out  by  the  field  observations  becomes 
more  intelligible  as  the  accumulating  data  define  more  clearly  the 
conditions  necessary  to  produce  the  remarkable  effects  observed. 
Thus  it  has  been  demonstrated,  not  only  in  the  field  but  also  in 
the  laboratory,  that  the  removal  from  the  soil  by  water  of  NaCl 
or  Na2S04,  together  with  the  water-soluble  products  of  their 
chemical  reaction  with  the  soil  constituents,  either  wholly  or  in 
part,  is  the  initial  step  in  creating  a  condition  favorable  for  the 
diffusion  of  the  soil  colloids  and  possibly  for  the  formation  of 
new  colloidal  matter.  Therefore  the  net  result  of  salt  application 
to  and  subsequent  washing  of  a  soil  is  to  render  the  soil  com- 
paratively impervious  and  to  injure  seriously  its  physical  con- 
dition. The  leaching  out  of  added  Na2C03  from  the  soil  also 
presents  some  interesting  phenomena,  which  are  discussed  below. 

Although  the  alteration  in  the  physical  condition  of  the  soil 
was  first  observed  by  the  writer  as  purely  incidental  to  an  investi- 
gation primarily  designed  to  ascertain  the  toxicity  limits  of  the 
common  alkali  salts  for  crop  plants,  yet  it  has  proved,  at  least 
in  the  case  at  hand,  a  most  perplexing  factor  in  the  production 
of  crops.  Our  experience  would  lead  us  to  believe  that  these 
after-effects  of  salt  treatments,  which  appear  during  the  course 
of  leaching  the  salts  from  the  soil,  would  have  some  application 
to  the  management  of  alkali  lands,  and  perhaps  some  significance 
with  respect  to  fertilizer  treatments.  However,  the  literature 
on  these  subjects,  with  a  few  exceptions,  seems  quite  devoid  of 
any  pertinent  reference  to  the  possible  importance  in  these 
problems  of  the  factor  discussed  above. 

A  survey  of  the  literature  concerning  soils  reveals  the  chief 
exceptions  just  mentioned  in  the  following  important  contribu- 
tions to  Hi  is  subject.  Thus,  a  brief  but  significant  chapter. 
' ' Veranderung  der  Durchlassigkeit  (lurch  Auswaschen  der 
Sake/'  by  Adolph  Mayer,1  records  a  somewhat  sudden  reduction 

•  Porschungen  auf  dem  Gebiete  der  Agrikultur-Physik,  vol.  2,  1879,  p.  251. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  293 

in  the  permeability  of  a  soil  when  NaOH  is  washed  from  it.  A 
similar  experiment  performed  by  Mayer  with  sodium  phosphate 
was  not  accompanied  with  the  sudden  reduction  in  permeability 
of  the  soil  as  was  noted  when  NaOH  was  washed  from  the  soil. 
Likewise  the  washing  out  of  lime-water  produced  no  marked 
effect  on  the  rate  of  percolation,  but  the  leaching  out  of  added 
NaCl,  either  with  pure  water  or  with  lime-water,  reduced  percola- 
tion to  a  minimum.  Mayer  ascribes  the  poor  physical  condition 
of  drained  sea-shore  lands  to  the  washing  out  of  the  salt,  and 
significantly  remarks  that  this  effect,  which  frequently  appears 
in  the  second  year,  is  probably  more  injurious  to  crop  plants 
than  the  toxicity  of  the  salt  itself. 

Van  Bemmelen2  in  his  classical  researches  on  colloids  has  also 
observed  a  similar  decrease  in  the  rate  of  percolation  when  loosely 
bound  salts  are  washed  from  clays  or  from  the  hydrated  oxides 
of  tin,  silica,  and  manganese.  Moreover,  he  noted  that  these 
colloids,  when  subjected  to  salt  treatments  followed  by  leaching 
with  water,  invariably  exhibited  a  high  degree  of  diffusion  upon 
suspension  in  water  for  a  second  time.  He  further  asserts  that 
this  process  can  be  indefinitely  repeated  by  alternately  adding 
to  and  washing  salt  from  the  colloids.  The  colloidal  particles, 
as  remarked  by  Van  Bemmelen,  become  so  exceedingly  small, 
during  the  process  of  washing  salts  from  them,  as  to  pass  through 
the  filter  paper. 

Warington3  also  refers  in  a  general  way  to  the  appearance 
of  somewhat  similar  phenomena  when  soils,  previously  treated 
with  acids,  are  washed  with  water. 

It  would  appear,  with  the  above  exceptions,  that  those  who 
have  studied  absorption,  adsorption,  or  other  physico-chemical 
effects  of  salts  on  soils,  have  failed  to  recognize  the  existence  of 
any  relation  between  the  washing  out  of  salts  and  the  subsequent 
condition  of  the  soil.  In  fact,  Hall  and  Morison4  assert  that  the 
flocculating  effect  of  salt  solutions  on  kaolin  are  reversible,  that 
is  to  say,  upon  the  removal  of  the  added  salt  the  kaolin  resumes 
the  original  condition  of  diffusion. 


2  Journ.  prakt.  Chem.,  2nd  ser.,  vol.  23,  p.  388,  1881. 

3  Physical  Properties  of  Soil  (Cambridge  Univ.  Press,  1900),  p.  30. 

4  Journ.  Agri.  Sci.,  vol.  2,  p.  244,  1907. 


294        University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

That  these  earlier  findings  have  a  greater  significance  in 
agricultural  practice  than  was  formerly  attributed  to  them  be- 
comes very  evident  when  the  practical  phase  is  attempted  of 
cropping  the  diffused,  salt-treated,  water-washed  soils  in  our 
cylinders.  Heretofore,  the  residual  effects  left  upon  clays  and 
clay  soils  after  salts  have  been  washed  from  them  have  been 
chiefly  considered  in  connection  with  their  application  to  the 
ceramic  industry,  and  have  been  largely  omitted  from  considera- 
tion by  those  dealing  with  soils. 

Since  the  striking  soil  behavior  under  discussion  was  first 
observed  by  us,  as  above  explained,  in  crop  cylinder  experiments, 
it  appears  desirable  to  introduce  here  a  brief  description  of  these 
experiments. 


The  Cylinder  Experiment  on  the  Physiological  Effects  of 
NaCl,  Na2S04  and  Na2C03  on  Crop  Plants 

The  cylinders  used  in  this  experiment  are  of  galvanized  iron, 
open  at  both  ends,  coated  inside  and  out  with  asphaltum,  and 
are  fourteen  inches  in  diameter  and  five  feet  long.  They  were 
placed,  during  September,  1913,  in  a  clay  loam  soil  at  Davis, 
California,  by  digging  holes  to  the  depth  of  five  feet.  During 
the  progress  of  digging  the  holes  the  soil  from  each  foot  was 
carefully  removed  and  set  aside  separately,  thus  permitting  the 
cylinders  to  be  refilled  with  the  soil  layers  in  the  same  order  as 
they  exist  naturally. 

The  soils  within  the  cylinders  were  then  supplied  with  vary- 
ing percentages  of  the  three  sodium  salts,  NaCl,  Na2SOt,  and 
Na2CO;r  It  seemed  a  difficult  task  to  secure  a  satisfactory  mixture 
of  the  salts  with  the  soil  already  in  the  cylinders,  and  it  was 
therefore  deemed  wise  to  apply  the  salts  to  the  surface  of  the 
soils  by  means  of  a  solution  containing  the  weighed  quantity 
of  salt  in  8800  cc.  of  distilled  water.  Accordingly,  each  cylinder 
received  the  same  quantity  of  water,  but  of  a  different  salt  con- 
centration.  In  addition  to  the  salts  some  of  the  soils  also  re- 
ceived other  treatments  which,  together  with  the  salt  treatments, 
are  detailed  in  the  following  chart.     The  quantities  of  salts  were 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  295 

calculated  and  applied  on  the  basis  of  percentage  of  weight  of 
the  five-foot  column  of  soil  in  every  cylinder. 

As  mentioned  above,  all  of  the  salt-treated  soils  developed 
every  indication  of  a  thoroughly  diffused  condition.  As  a  result, 
percolation  through  the  treated  cylinders  practically  ceased,  so 
that  the  rain-water  collected  in  the  two-inch  cylinder  rim  and 
remained  so  persistently  as  to  prove  seriously  detrimental  to  the 

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Fig.  1.     The  Salt  and  Manure  Applications  to  the  Soil  in  the 

Cylinders   at   Davis. 

The    upper    figures    refer    to    the    percentages    of    salts    in    the    5-foot 

column  of  soil.     The  lower  figures  refer  to  the  grams  of  barnyard  manure 

added.     In  row  1,  no.  1  contains  Na2S04  instead  of  NaCl.     In  row  10,  no. 

2  likewise  contains  Na2S04  instead  of  Na2C03. 

growth  of  crops.  As  a  final  measure,  holes  were  opened  down 
through  the  soil  columns  to  provide  drainage.  In  sharp  contrast 
with  the  treated  soils,  even  immediately  after  heavy  rain-storms, 
no  standing  water  was  ever  observed  on  the  control  soils,  and 
the  splendid  growth  of  the  crops  planted  on  them  showed  a  con- 
genial  condition   for   crop   development.      Both   the   winters   of 


296         University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

1913-14  and  1914-15  were  accompanied  with  similar  manifesta- 
tions of  the  extreme  retentiveness  and  imperviousness  of  the  salt- 
treated  soils. 

As  previously  remarked,  all  of  the  check  soils  responded 
readily  to  cultivation  and  excellent  seed  beds  were  easily  pre- 
pared, while  the  soils  to  which  NaCl  and  Na2S04  had  been  added 
were  in  an  unworkable  condition.  A  crust,  an  inch  or  so  in 
thickness,  formed  as  soon  as  the  surface  dried,  and  was  so  hard 
that  even  heavy  tools  made  but  little  impression  on  it.  Just 
below  the  crust  the  soil  was  far  too  wet  for  plant  roots  and  re- 
sembled putty  in  consistency.  Contrary  to  expectations,  the 
soils  treated  with  Na2C03  exhibited  better  cultivating  qualities 
than  the  soils  receiving  the  other  salts,  but  inferior  to  those 
of  the  control  soils. 

With  a  view  to  obtaining  further  information  concerning  the 
great  dissimilarity  between  the  control  soils  and  the  salt-treated 
soils,  it  seemed  wise  to  examine  some  of  the  surface  water  stand- 
ing in  the  cylinders  as  well  as  the  soil  in  contact  therewith.  These 
proved  to  contain  but  mere  traces  of  any  salts.  Of  next  im- 
portance a  study  of  the  vertical  distribution  of  the  salts  in  the 
cylinders  disclosed  the  fact  that  the  first  few  inches  of  soil 
contained  relatively  small  quantities  of  the  salts,  the  first  foot 
more,  the  second  still  more,  and  the  third  foot  most  salt.  From 
these  results  it  was  concluded  that  the  addition  of  NaCl  or  Na2S04 
to  a  soil  and  subsequently  washing  the  added  salt,  or  at  least 
part  of  it,  from  the  soil  with  water,  produces  a  high  degree  of 
diffusion  in  the  soil  colloids.  Moreover,  this  alteration  in  diffusion 
was  accompanied  with  proportional  changes  in  the  other  physical 
characteristics  of  the  soil.  These  conclusions  based  on  our  field 
experience  were  soon  verified  by  laboratory  experiments. 

Laboratory  Experiments  Reproducing  Field  Observations 

It  has  been  found  that  the  field  conditions  can  be  readily 
reproduced  in  the  laboratory.  Thus  a  simple  procedure,  illustrat- 
ing qualitatively  the  lessened  percolation,  is  to  place  10  grams  or 
more  of  soil  in  a  filter  paper  in  a  funnel,  adding  thereto  either 
NaCl  or  Na2S04  as  a  solid  or  in  a  water  solution,  and  then  wash- 


1916] 


Sharp:  Soluble  Salts  and  Soil  Colloids 


297 


ing  the  soil  practically  free  of  salt,  meanwhile  washing  with 
pure  water  a  similar  portion  of  soil  from  v/hich  the  salt  has 
been  omitted  to  serve  as  a  control.  The  difference  in  the  rate  of 
percolation  of  the  two  soils  has  proved  to  be  sufficiently  great  to 
be  easily  discernible  even  in  the  case  of  sandy  soils.    Frequently 


108144     180     216    252    286    324    360    396    432    468    504   540  576 

""• •  »   1 • 1 r~ -t— 1 1 1 1 1 1 


Fig.  2.     Curves  Representing  the  Downward  Movement  of  Water  Through 
the  Davis   Soil  to  which   Salts   Have  Been   Added. 
The  penetration  of  the  water  downward  in  the  soil  column  is  expressed 
in   inches   by  the   ordinates,   while  the   abscissas   represent   the   time    of 
observations  in  hours. 


the  fine  material  mentioned  by  Van  Bemmelen  and  Warington 
appears  in  the  percolate. 

It  has  also  been  found  possible  to  simulate  fairly  the  condi- 
tions existing  in  the  field  cylinders  by  means  of  glass  tubes  care- 


298         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

fully  filled  with  the  Davis  clay  loam  to  which  chemically  equiva- 
lent salt  solutions  were  added,  much  in  the  same  manner  as  the 
salt  applications  were  made  to  the  cylinder  soils.  A  constant 
head  of  water  was  then  carefully  maintained  in  the  tubes.  The 
downward  movement  of  the  water  was  observed  from  time  to 
time  and  is  graphically  portrayed  in  Figure  2. 

From  the  curves  in  it  it  is  very  apparent  that  the  influence  of 
these  salt  additions,  accompanied  by  subsequent  surface  applica- 
tions of  water  to  the  soil,  has  been  to  retard,  markedly,  the  down- 
ward movement  of  the  water  through  the  soil.  In  less  than  33 
hours  the  water  had  penetrated  the  entire  14^2  inches  of  soil  in 
the  control  tube,  while  at  the  end  of  552  hours,  under  a  constant 
head  of  three  inches,  the  maximum  distance  reached  in  any  of 
the  salt-treated  soils  was  13%  inches  in  the  case  of  the  soil 
receiving  NaCl,  followed  by  13*4  inches  in  the  Na2C03  soil,  and 
but  11  inches  in  the  soil  to  which  Na2S04  had  been  added.  At 
the  expiration  of  56  days  no  percolation  had  occurred,  though 
the  entire  soil  columns  were  moist.  The  total  absence  of  percola- 
tion in  the  salt-treated  soils  was  attributed  to  the  growth  of  algae 
in  the  tubes. 

To  test  further  the  points  under  consideration,  a  second  series 
was  prepared  to  study  the  rates  of  percolation  through  Davis 
clay  loam  to  which  salts  had  been  added  in  various  ways.  The 
results  of  this  experiment  are  embodied  in  Table  I. 

In  the  above  experiment  the  chemically  equivalent  quantities 
of  salts  were  mixed  uniformly  with  the  dry  soil  before  placing 
the  mixture  in  the  paramne-coated  brass  percolation  tubes,  except 
in  the  case  of  Nos.  12,  13,  and  14,  through  which  salt  solutions 
were  passed  of  a  strength  (calculated  on  the  basis  of  a  previously 
determined  water-holding  power  of  the  soil)  to  give  compara- 
tively equal  quantities  of  salts  with  those  soils  receiving  the  dry 
salts.  A  head  of  one  to  two  inches  was  carefully  maintained  on 
the  soil  in  all  the  tubes  throughout  the  experiment. 

The  results  recorded  in  the  foregoing  table  fully  corroborate 
the  field  experience.  Thus,  the  average  rate  of  percolation  of 
the  check  soil  was  1.59  cc.  per  hour,  while  that  of  the  soil  to 
which  NaCl  has  been  added  was  reduced  to  .19  cc.  per  hour.  The 
percolation    through   the   other  two   soils   which    received  solid 


1916] 


Sharp:  Soluble  Salts  and  Soil  Colloids 


299 


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300         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

Na2S04  and  Na2C03  was  also  decidedly  reduced,  as  shown  by 
the  respective  percolation  rates  of  .31  cc.  and  .37  cc.  per  hour.  In 
significant  contrast  thereto,  the  maintenance  of  a  comparatively 
uniform  salt  content  in  the  soil  column,  produced  by  substituting 
solutions  of  the  salts  for  the  distilled  water  as  in  the  case  of 
Nos.  12,  13,  and  14,  creates  a  favorable  condition  for  percolation, 
except  in  No.  14,  which  received  Na2C03.  In  this  case  percola- 
tion averaged  a  rate  of  1.07  cc.  per  hour,  which  was  less  than  the 
control,  but  three  times  that  of  the  soil  receiving  Na2C03  and 
distilled  water.  It  is  of  interest  to  note  the  immediate  depression 
in  the  rate  of  percolation  when  distilled  water  is  used  instead  of 
the  salt  solutions  of  Nos.  12,  13,  and  14.  Eventually  the  rate  of 
percolation  from  these  soils  under  applications  of  distilled  water 
approached  that  of  the  soils  originally  treated  with  salts  and 
which  in  addition  had  received  only  distilled  water  throughout 
the  experiment. 

Another  percolation  experiment,  arranged  somewhat  similarly 
to  the  preceding,  demonstrated  that  the  relative  position  of  the 
salt  in  the  soil  column,  or  the  manner  of  adding  it,  had  little  or 
no  influence  on  the  depressing  effect  noted  on  percolation.  It  was 
further  observed  that  a  soil,  the  percolation  rate  of  which  had 
been  diminished  through  the  agency  of  NaCl  and  H20  applica- 
tions, failed  to  recover  its  original  rate  of  percolation  even  when 
a  solution  of  that  salt  was  applied  for  the  second  time. 

The  general  trend  of  the  results  thus  far  secured  is  in  accord 
with  Beeson's  observations,5  in  which  he  recorded  a  delayed 
absorption  of  water  by  soils  containing  sodium  salts  as  well  as 
a  pronounced  retarding  of  percolation  through  soils  to  which 
various  salts  had  been  added.  Like  many  other  investigators 
who  have  observed  similar  effects  resulting  from  salt  treatments, 
Beeson  failed  to  recognize  any  connection  between  the  physical 
condition  of  the  soil  and  the  removal  of  the  salt,  but  attributed 
the  peculiar  changes  observed  in  the  soil  to  surface-tension 
phenomena,  or  other  alterations  in  the  physical  properties  of  the 
liquid  phase,  or,  as  some  investigators  are  inclined  to  believe, 
to  a  shifting  of  the  soil  particles  to  new  positions  through  the 
influence  of  the  added  salt.     Undoubtedly  a  movement  of  soil 


BJourn.  Am.  Chem.  Soc,  vol.  29,  p.  620,  1897. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  301 

particles  does  occur  when  salts  are  added  to  soils,  but  under  the 
conditions  obtaining  in  many  of  the  experiments  described  in  the 
literature  it  would  seem  highly  improbable  that  enough  of  the 
added  salt  remains  in  contact  with  the  soil  to  bring  about  such 
a  movement  of  the  particles.  In  our  experience,  the  removal  of 
the  salt  creates  among  the  soil  particles  a  new  adjustment  which 
seems  of  greater  importance  than  that  effected  by  the  addition 
of  the  salt.  Furthermore,  if  our  laboratory  experience  is  properly 
applicable  to  field  conditions,  it  would  seem  of  greater  advantage 
to  apply  CaC03  rather  than  CaS04  when  draining  soils  contain- 
ing NaCl  and  Na2S04,  the  reverse  being  apparently  true  in  case 
of  soils  impregnated  with  Na2C03. 

Laboratory  Investigations  of  the  Causes  of  Salt 
Effects  on  Soils 

The  laboratory  studies  herein  reported  have  been  purposely 
designed  to  throw  some  light  on  the  possible  causes  contributing 
to  the  above-noted  effects  of  salts  on  soils,  or  at  least  to  ascertain 
if  a  relationship  exists  between  the  formation  of  these  peculiar 
physical  conditions  and  the  simultaneous  occurrence  of  certain 
other  events.  Certain  well-known  theoretical  considerations,  re- 
inforced by  concrete  laboratory  experience,  have  directed  the 
attempts  to  locate  these  fundamental  causes  into  three  well- 
defined  channels.  The  first  of  these  is  based  on  an  assumption 
that  the  salt-and-wTater  treatments  have  actually  increased  the 
quantity  of  the  colloidal  matter  of  the  soil.  It  involves  neces- 
sarily a  study  of  the  soil  itself  and  of  the  amount  and  degree  of 
diffusion  of  the  colloidal  matter  therein  contained.  The  second 
line  of  reasoning  connects  the  increase  of  calcium  and  magnesium 
in  the  percolate  from  the  salt-treated  soils,  and  the  absorption  of 
sodium,  with  the  appearance  of  conditions  suitable  for  the 
formation  of  new  colloidal  matter,  as  well  as  with  favoring  the 
extreme  diffusion  of  that  already  present.  The  third  considera- 
tion ascribes  the  diffused  condition  of  the  soil  colloids  to  the 
presence  of  a  small  quantity  of  OH-ions  in  the  soil  solution.  It 
requires  the  theoretical  assumption  that  these  ions  are  associated 
in  some  manner  with  the  absorption  of  sodium.    Although  these 


302         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

three  lines  of  argument,  as  outlined,  may  be  closely  allied  or  even 
parallel,  yet  in  view  of  our  work  they  seem  sufficiently  well  de- 
fined to  warrant  a  separate  discussion  of  each. 

At  the  outset  it  may  be  said  that  it  has  been  extremely  diffi- 
cult to  find  appropriate  and  reliable  methods  of  attacking  this 
problem.  Certainly  opportunity  is  not  lacking  for  future  in- 
vestigations to  perfect  accurate  methods  for  definitely  measuring 
certain  soil  properties  or  soil  constants,  which  are  discussed 
below.  The  Davis  clay-loam  soil  was  used  throughout  the  fol- 
lowing experiments,  except  as  otherwise  noted.  The  designation 
NaCl  +  H20  used  before  the  word  soil  signifies  that  the  soil 
was  treated  with  from  0.2  to  0.5  per  cent  of  NaCl,  most  or  all 
of  which,  together  with  the  soluble  salts  formed,  has  been  subse- 
quently leached  from  the  soil  with  water.  It  must  be  added  that 
a  quantity  of  Davis  clay-loam  soil  was  given  the  same  amount 
of  washing  with  water  to  serve  as  a  control  soil,  and  hereafter 
will  be  referred  to  as  H20  soil.  A  comparison  of  the  H20  soil 
with  unwashed  Davis  soil  disclosed  no  important  differences. 

Some  Physico-Chemical  Observations  on  the  Salt-Treated, 
Water-Washed  Soil 

It  seemed  reasonable  to  expect  that  a  study  of  the  NaCl  +  H20 
soil  itself  would  reflect,  in  some  degree,  the  causes  contributing 
to  the  pronounced  imperviousness  of  such  soils.  Therefore,  as 
an  introduction  to  this  subject,  determinations  were  made  of  the 
suspended  matter  derived  from  soils  which  have  been  subjected 
to  various  treatments,  and  they  appear  in  Table  II.  The  soils 
and  suspending  media  were  placed  together  in  tall  hydrometer 
jars,  and  were  thoroughly  shaken  for  45  minutes.  After  standing 
undisturbed  for  eighteen  hours,  aliquot  portions  of  the  sus- 
pensions were  removed  by  means  of  a  pipette,  evaporated  to 
dryness  in  platinum  dishes,  dried  at  110°  C,  and  weighed. 

The  data  reported  in  Table  II  confirm  by  an  entirely  different 
procedure  the  original  belief  with  respect  to  the  intensity  of  the 
diffusion  of  the  colloids  of  the  salt-treated,  water-washed  soils. 
Under  the  conditions  of  the  experiment  40  grams  of  normal  soil 
yielded   0.310  grams  of  suspended  matter,  while  40  grams  of 


1916]                          Sharp:  Soluble  Salts  and  Soil  Colloids  303 

TABLE  II 

Suspended  Matter  in  Soils  Which  Have  Received  Various  Treatments 

Per  cent  of 

Weight  of  Suspended 

Previous                     Suspending                  Suspended  Matter 

No.     Davis  Soil            Soil  Treatment                  Medium                     Matter-grs.  in  soil 

1  40  grs.       Washed  with  dis- 

tilled water                     H20                       .3100  .77 

2  40  grs.       Boiled  in  H20                     H20                     2.5075  6.27 

3  40  grs.       .290  grs.  of  NaCl 

washed  out                       H20                     2.9555  7.39 

4  40  grs N/50Na2CO3               .2665  .66 

5  40  grs N/50NaOH              2.7975  6.99 


NaCl  -j-  H20  soil  yielded  2.9555  grams,  or  nearly  ten  times  the 
amount  of  suspended  matter  found  in  the  untreated  soil.  It  is 
an  interesting  coincidence  that  the  rate  of  percolation  previously 
shown  for  the  untreated  soil  is  almost  ten  times  that  for  soil 
to  which  NaCl  has  been  added  and  subsequently  leached  out.  It 
may  be  properly  inferred  from  this  that  percolation  varies  in- 
versely as  the  degree  of  diffusion,  though  our  present  knowledge 
does  not  indicate  a  relation  capable  of  expression  in  simple 
mathematical  terms.  Furthermore,  the  inadequacies  of  the 
method  employed  to  secure  the  data  in  Table  II  make  it  impos- 
sible to  express  a  positive  view  with  reference  to  the  quantity  of 
colloids  in  the  soils  tested,  but  it  is  evident  that  the  colloidal 
matter  present  is  in  a  much  higher  state  of  diffusion  in  certain 
of  the  soils  than  in  the  control  H20  soil.  The  three  treatments, 
boiling  the  soil  in  water,  suspending  it  in  NaOH  of  certain  con- 
centrations, and  leaching  added  NaCl  from  it,  produce  approxi- 
mately the  same  degree  of  diffusion  in  the  soil  colloids,  as  indi- 
cated by  the  similarity  in  the  results  of  the  quantitative  esti- 
mations of  the  suspended  matter  derived  from  soils  so  treated. 
This  agreement  in  the  behavior  of  the  soils  receiving  the  different 
treatments  suggests  a  similarity  or  possible  relationship  between 
the  processes  by  which  these  treatments  affect  the  soil  or  soil 
colloids.  Boiling  the  soil  in  water  has  been  assumed  b}r  soil 
physicists  to  disintegrate  the  colloidal  aggregates.  If  this  be  the 
case  and  no  new  colloidal  substances  are  formed  by  this  pro- 
cedure, then  the  similarity  in  colloidal  content  of  the  boiled  soil 
and  the  salt-treated,  water-washed  soil  militates  against  the  sup- 


304        University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

position  that  the  latter  treatment  has  increased  the  colloidal 
matter  of  the  soil.  On  the  other  hand,  boiling  the  soil  in  water 
may  bring  about  a  more  profound  change  in  the  physical  condi- 
tion of  the  soil  than  was  formerly  attributed  to  it  by  soil 
physicists.  Some  data  withheld  from  publication  at  this  time 
indicate  that  the  effect  of  the  boiling  treatment  is  of  a  different 
nature  from  that  of  the  salt-and-water  treatment,  though  the 
soils  receiving  the  two  different  treatments  yield  about  the  same 
quantity  of  colloidal  matter.  On  the  other  hand,  the  similarity 
of  the  colloidal  contents  of  the  boiled  soil  and  the  soil  suspended 
in  NaOH  admits  of  a  more  plausible  explanation  on  the  basis 
of  NaOH  as  a  deflocculating  agent. 

It  was  thought  that  the  quantitative  data  reported  above 
might  show  sufficient  dissimilarity  to  indicate  an  actual  increase 
in  the  soil  colloids,  but  a  second  series  of  determinations,  reported 
in  a  later  paragraph,  are  somewhat  contradictory  to  the  above,  in 
that  the  boiled  soil  yields  a  suspension  slightly  richer  in  colloidal 
matter  than  that  derived  from  a  NaCl  +  H20  soil.  This  point, 
however,  deserves  more  investigation  before  a  final  conclusion  is 
reached. 

In  the  light  of  certain  theories  more  properly  discussed  in 
connection  with  the  third  hypothesis,  it  is  of  great  interest  to 
note  the  general  similarity  between  the  NaCl  +  H20  soil  when 
suspended  in  H20  and  the  normal  soil  when  suspended  in  NaOH. 
One  might  infer  that  this  peculiar  agreement  in  the  behavior  of 
the  soils  in  response  to  two  widely  different  treatments  is  not 
accidental.  It  is  also  to  be  observed  further  that  the  data  under 
consideration  indicates  that  NaOH  and  Na2C03  are  not  pro- 
ductive of  like  results  on  soil  suspensions. 

The  failure  of  the  suspension  method  to  secure  trustworthy 
results  on  the  quantity  of  colloidal  matter  present  prompted  the 
adoption  of  other  means  for  this  purpose.  But  thus  far  the 
determination  of  the  hygroscopic  coefficient  and  the  dye- 
adsorption  capacity  have  given  negative  results,  in  that  they  have 
not  indicated  any  increase  in  the  total  interior  surface  of  the 
soils  which  have  been  subjected  to  the  salt  treatments.  From  a 
theoretical  consideration,  a  soil  rich  in  colloids,  or  containing 
colloids  in  a  high  state  of  diffusion,  should  expose  more  interior 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  305 

surface  for  the  deposition  of  hygroscopic  moisture  and  for  dye 
adsorption,  and  since  these  phenomena  are  presumably  direct 
functions  of  surface  the  soils  under  observation  should  therefore 
register  increased  hygroscopicity  and  dye  adsorption.  The  find- 
ings to  the  contrary  cast  some  doubt  on  the  validity  of  these 
measurements  as  a  reflection  of  the  quantity  of  colloidal  matter 
present  or  its  degree  of  diffusion.  A  third  method  suggests 
itself,  that  developed  by  Mitscherlich,6  to  study  the  interior  sur- 
face through  energy  exchanges  when  the  soil  is  moistened  with 
water,  but  this  has  not  as  yet  been  tried. 

The  use  of  the  centrifugal  machine  as  employed  by  Briggs 
and  McLane7  to  ascertain  the  moisture  equivalent  of  soils  in  the 
study  of  the  salt-treated,  water-washed  soils,  has  yielded  some 
highly  satisfactory  results  which  will  be  reported  in  a  future 
paper.  The  method  proposed  by  Lynde  and  Dupre8  for  esti- 
mating the  capillary  powers  of  soils  has  not  proven  entirely 
satisfactory  in  our  hands,  when  employed  for  investigating  the 
properties  of  the  salt-treated  soils. 

It  was  further  questioned  whether  the  physical  condition  of 
the  soil  had  been  permanently  changed  or  whether  the  injured  soil 
would  completely  recover  its  original  condition  in  response  to  a 
second  addition  of  NaCl.  Such  a  supposition  naturally  implies 
that  some  of  the  reactions  involved  in  producing  the  increased 
diffusion  partake  of  the  nature  of  reversible  reactions.  In  order 
to  test  this  point  from  a  chemical  standpoint,  it  would  be  neces- 
sary to  treat  the  injured  soil  with  its  own  percolate.  Work  of 
this  character  is  reported  under  the  second  series  of  experiments. 
In  this  connection,  however,  the  effects  of  the  added  salts  were 
considered  chiefly  in  their  physical  aspects,  and  accordingly  the 
following  experiment  was  performed :  Three  grams  of  NaCl  -4- 
H20  soil  were  suspended  in  10  cc.  of  NaCl  solutions  of  various 
concentrations  in  test-tubes.  The  time  required  to  clear  the 
supernatant  liquid  denoted  the  effect  of  the  NaCl.  A  similar 
comparative  series  with  H20  soil  was  also  prepared.  The  results 
are  given  in  Table  III. 


G  Bodenkuncle  fiir  Land-  und  Forstwirte,  p.  51. 

7  U.  S.  Dept.  Agr.,  Bur.  of  Soils,  Bull.  45. 

s  Journ.  Amer.  Soc.  Agron.,  vol.  5,  no.  2,  p.  107,  1913. 


306         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 


TABLE  III 

Effect  of  Second  Addition  of  NaCl  on  Time  Eequired  to  Clear 
Suspensions  of  NaCl  4-  H20  Soil  and  H20  Soil 


No. 

1 
2 
3 
4 
5 
6 


9 
10 
11 
12 
13 


Soil 
3grs. 
3grs. 
3  grs. 
3grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 
3  grs. 


Previous 
Treatment 

NaCl  washed  out 

NaCl  washed  out 

NaCl  washed  out 

NaCl  washed  out 

NaCl  washed  out 

NaCl  washed  out 

H20  washed 

H,0  washed 

H20  washed 

H20  washed 

H20  washed 

HoO  washed 


Concentration 

of  NaCl  as 

Suspending 

Medium 


N/1000 

N/500 
N/250 
N/100 

N/50 

N/1000 
N/500 

N/250 
N/100 

N/50 


Time  Required  to 
Clear  Suspension 

Almost  clear  after  600  hrs. 

Almost  clear  after  600  hrs. 

Almost  clear  after  600  hrs. 

Clear  after  600  hrs. 

Clear  after  360  hrs. 

Clear  after    20  hrs. 

Clear  after  164  hrs. 

Clear  after  140  hrs. 

Clear  after  117  hrs 

Clear  after    53  hrs. 

Clear  after      1  hr. 

Clear  after    y3  hr. 

Clear  after  140  hrs. 


The  results  of  this  experiment  seemed  of  sufficient  interest 
to  warrant  a  repetition  of  the  work  on  a  larger  scale.  Accordingly 
the  following  experiment  was  prepared,  much  in  the  same  manner 
as  the  above,  but  using  25  grams  of  soil,  250  cc.  of,  solution,  and 
250  cc.  graduates,  instead  of  test  tubes.  In  this  case  the  weight 
of  the  suspended  matter  was  also  determined  after  the  mixtures 
had  stood  undisturbed  for  three  days.  A  photograph  of  this 
series  taken  two  days  after  the  final  shaking  is  shown  (Figure  3). 


;j 


Pig.  3.     A  Photograph  of  the  Suspensions  Described  in  Table  IV 
The  graduates  containing  the  suspensions  as  shown  in  Figure  3   cor- 
respond, from  left  to  right,  to  the  Nos.  1  to  12,  inclusive,  of  Table  IV. 


1916] 


Sharp:  Soluble  Salts  and  Soil  Colloids 


307 


TABLE  IV 

Effect  of 

Second  Addition  of 

NaCl  ON  THE 

Amounts  of  Suspended  Matter 

From  NaCl  +  H20  Soil  and  H20 

Soil 

No. 

Soil 

Previous 
Treatment 

Concentration 

of  NaCl            Cc.  of 

Suspending  Suspending 

Solution         Medium 

Weight  of 
;     Suspended 
Matter 

Per  cent 

of 

Suspended 

Matter 

on  Dry 

Soil 

1 

25  grs. 
25  grs. 

NaCl  washed  out 

250 

.8345  grs. 
.6375 

3.33 

2 

NaCl  washed  out 

N/1000 

250 

2.55 

3 

25  grs. 

NaCl  washed  out 

N/500 

250 

.5615 

2.36 

4 

25  grs. 

NaCl  washed  out 

N/250 

250 

.4570 

1.82 

5 

25  grs. 

NaCl  washed  out 

N/100 

250 

.2305 

.92 

6 

25  grs. 

NaCl  washed  out 

N/50 

250 

.0170 

.07 

7 

25  grs. 
25  grs. 

H20  washed 
H20  washed 

250 

.0695 

.27 

8 

N/1000 

250 

.0740 

.29 

9 

25  grs. 

H20  washed 

N/500 

250 

.0660 

.26 

10 

25  grs. 

H20  washed 

N/250 

250 

.0615 

.24 

11 

25  grs. 

H20  washed 

N/100 

250 

Lost,  but  al- 
most clear 

12 

25  grs. 

H20  washed 

N/50 

250 

13 

25  errs. 

Boiled 

250 

.9060 

3.62 

The  evidence  presented  in  the  last  two  tables  supports  the 
view  that  the  NaCl  -f-  H20  soil  has  suffered  some  physical  altera- 
tion which  is  not  readily  reversed  by  the  second  addition  of 
NaCl.  The  NaCl  added  to  the  soil  already  diffused  by  previous 
treatment  with  that  salt  and  water  is  here  considered  as  a 
physical  agent,  possessing  the  power  to  flocculate  clay  colloids. 
To  test  the  reversibility  of  the  chemical  reactions  occurring  when 
salt  solutions  are  allowed  to  act  upon  soils  requires  a  soil  treat- 
ment involving  the  application  of  solutions  containing,  in  appro- 
priate form  and  quantity,  the  elements  removed  by  the  salt  ap- 
plications. Thus,  to  restore  normal  conditions  in  a  soil  which  has 
been  diffused  by  a  salt-and-water  treatment  would  require  the 
replacement  of  the  absorbed  sodium  by  such  metals  as  were 
originally  present  in  the  soil.  The  larger  amounts  of  NaCl  re- 
quired to  flocculate  the  colloids  of  the  diffused  soil  may  be  due 
to  the  increased  quantity  of  colloids  present,  or  to  the  degree  of 


308         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  I 

diffusion  of  the  colloids,  or  to  a  change  in  the  nature  of  the 
colloid.  However,  the  fact  is  patent  that  more  NaCl,  or  a 
greater  length  of  time  for  equal  quantities  of  NaCl,  is  required 
to  produce  effects  on  the  NaCl  +  H20  soil  commensurate  with 
those  on  the  check  H20  soil.  Table  III  shows  clearly  the  relative 
effectiveness  of  varying  concentrations  of  NaCl  in  flocculating 
the  colloidal  matter  as  measured  by  the  time  required  for  clearing 
the  suspension.  Thus  N/100  NaCl  flocculates  the  colloidal  matter 
of  the  washed  soil  in  one  hour,  while  360  hours  were  required  to 
accomplish  the  same  result  with  the  NaCl  -f-  H20  soil.  Never- 
theless, the  colloidal  matter  of  the  NaCl  -f-  H20  soil  seems  to  be 
more  readily  flocculated  per  unit  of  NaCl  than  does  that  of  the 
H20  soil,  as  is  shown  in  Table  IV.  Thus  the  NaCl  +  H20  soil, 
when  suspended  in  distilled  water,  yields  a  suspension  containing 
0.8345  grs.  of  solid  matter,  while  the  same  soil  suspended  in  N/250 
NaCl  yields  but  0.4570  grs.  of  solid  matter.  The  deposition  of 
0.3775  grs.  of  solid  matter,  in  this  case,  was  brought  about  by 
0.058  grs.  of  NaCl,  or  at  the  rate  of  6.5  mgs.  of  solid  matter  to 
1  mg.  of  NaCl.  Similar  calculations  for  the  same  suspensions 
of  H20  soil  showed  that  but  0.14  mgs.  of  suspended  matter  was 
flocculated  per  mg.  of  NaCl.  Although  the  NaCl  is  relatively 
more  effective  on  the  suspended  matter  of  the  NaCl  +  H20  soil 
than  on  that  of  the  control  soil,  yet,  in  but  one  instance,  that  of 
the  comparatively  strong  solution  of  N/50  NaCl,  is  the  influence 
of  the  added  salt  sufficient  to  flocculate  completely  the  colloidal 
matter  of  the  NaCl  -f-  H20  soil. 

Furthermore,  it  seemed  possible  that  the  transformations 
manifestly  occurring  in  the  physical  condition  of  the  soil  might 
also  be  reflected  in  some  measure  in  the  chemical  composition  of 
the  variously  treated  soils  and  of  their  colloidal  substances.  Ac- 
cordingly these  materials  were  subjected  to  analysis  by  the  strong 
hydrochloric-acid  digestion  method,  as  recommended  by  Hilgard 
for  chemical  soil  studies.  However,  the  results  secured  up  to 
the  present  time  have  not  confirmed  the  above  presumption.  But 
to  what  extent  future  analytical  work  will  enable  us  to  decipher 
the  relationship  of  the  various  factors  involved  in  producing  the 
condition  under  consideration,  is  still  an  open  question. 


1916] 


Sharp:  Soluble  Salts  and  Soil  Colloids 


309 


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310        University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

Chemical  Studies  of  the  Calcium  and  Magnesium  Content  of  the 
Percolate  and  the  Absorption  of  Sodium 

Our  attention  was  first  directed  to  the  possibility  of  the  ex- 
istence of  a  relationship  between  the  two  factors  mentioned  in 
the  heading  above,  by  the  following  experiment,  the  outline  and 
results  of  which  appear  in  Table  V,  page  309. 

A  review  of  these  data  discloses  the  fact  that  the  application 
of  NaCl  to  a  soil  increases  the  calcium  and  magnesium  found  in 
the  percolate  as  compared  with  the  quantities  found  in  the 
percolate  of  the  normal  soil  when  leached  with  distilled  water. 
This  is  in  accord  with  the  results  of  Kullenberg,9  Van  Bem- 
melen10  and  the  work  of  others,  a  good  list  of  which  is  given  by 
Sullivan.11  To  exemplify  the  above  remarks  concerning  calcium, 
let  us  examine  the  table  with  respect  to  that  element.  The  addi- 
tion of  NaCl  to  the  Anaheim  sandy  loam  and  Oakley  sandy  soil 
has  practically  tripled  and  doubled,  respectively,  the  amount  of 
calcium  found  in  the  percolates  over  that  of  the  percolate  from 
the  salt-free  soil.  In  the  Berkeley  adobe  and  Davis  clay-loam  soils 
the  NaCl  brings  about  a  much  more  marked  increase  of  calcium 
in  the  leachings.  It  may  be  remarked  also  that  the  results  secured 
with  magnesium  are  quite  parallel  to  those  concerning  calcium. 

In  addition  to  altering  the  calcium  and  magnesium  contents 
of  the  percolate,  the  salt  treatments  materially  affected  the  physi- 
cal condition  of  the  soil,  as  shown  by  a  marked  retardation  of  the 
rate  of  percolation.  All  of  the  soils  responded  alike  to  the  NaCl 
treatments,  in  that  they  became  more  impervious  and  their  col- 
loidal matter  exhibited  a  higher  degree  of  diffusion  when  sus- 
pended in  water,  as  shown  in  the  second  part  of  Table  V.  The 
degree  of  imperviousness  and  diffusion  varied,  however,  with 
the  different  soils,  and  also  appeared  to  be  roughly  proportional 
to  the  increase  of  calcium  and  magnesium  in  the  leachings  from 
the  soils  receiving  NaCl.  Thus  the  salt-treated  Berkeley  and 
Davis  soils,  showing  notably  greater  increases  in  calcium  and 
magnesium  in  the  percolates,  were  also  more  highly  diffused  than 


9  Jahrb.  Fortsch.  Agri.  Chem.,  vol.  8,  p.  15,  1865. 
loLandw.  Vers.  Stat.,  vol.  21,  p.  135,  1878. 
"  U.  S.  Geol.  Surv.,  Bull.  312,  1907. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  311 

the  other  two  soils,  which  were  much  less  affected  in  both  these 
particulars.  Evidently  the  extent  of  decomposition  of  the  salt 
by  the  soil  is  a  factor  in  determining  the  final  physical  condition 
thereof,  and  would  certainly  seem  to  indicate  that  the  changes  of 
the  physical  condition  of  the  soil  resulting  from  salt  treatments 
are  considerably  more  than  a  mere  shifting  of  the  soil  particles 
to  new  positions,  as  some  investigators  would  lead  us  to  believe. 
Moreover,  it  appears  proper  to  infer  that  these  after-effects  of  salt 
treatments  can  be  more  properly  referred  to  the  salt  as  a  chemical 
agent  than  as  a  physical  agent. 

If  it  be  true  that  the  chemical  reaction  between  soils  and  salt 
solutions  results  in  a  chemically  equivalent  exchange  of  bases,  as 
Sullivan12  states,  then  it  seems  proper  to  assume  that  the  calcium 
and  magnesium  in  the  leachings  from  soils  treated  as  described 
above  represent  approximately  the  amount  of  absorbed  sodium. 
At  least  it  would  appear  that  the  calcium  and  magnesium  in  the 
solutions,  less  the  quantity  normally  present  in  distilled-water 
extractions,  is  an  index  of  the  absorbed  sodium.  This  statement 
has  received  further  justification  in  some  solubility  studies,  the 
data  of  which  have  not  been  published.  Undoubtedly  consider- 
able quantities  of  sodium  have  been  removed  from  the  salt  solu- 
tions by  the  soil,  which  in  return  has  given  up  calcium  and  mag- 
nesium. The  absorbed  sodium  has  become  so  firmly  fixed  in  the 
soil  that  no  amount  of  washing  can  dissolve  it;  otherwise  the 
wash  water  after  passing  through  the  soil  would  be  slightly  alka- 
line. On  the  contrary,  the  first  portions  of  the  wash  water  com- 
ing through  appear  to  be  slightly  acid,  which  is  in  accord  with 
the  work  of  Sullivan,13  Parker,14  and  others,  but  if  the  washing 
is  continued  the  leachings  eventually  become  neutral  or  just  per- 
ceptibly alkaline,  as  is  the  case  when  distilled  water  is  in  contact 
with  the  normal  Davis  soil.  These  remarks,  supported  with 
stronger  evidence  from  the  rapidly  accumulating  literature  on 
chemical  exchanges  between  salt  solutions  and  soils  or  silicates, 
point  to  the  formation,  under  the  conditions  herein  reported,  of 
a  sodium  alumino-silicate  compound,  or  possibly  a  series  of  such 


12  Loc.  cit.,  p.  27. 

is  Loc.  cit.,  p.  8. 

14  Journ.  Agric.  Eesearch,  vol.  1,  no.  3,  p.  1,  1913. 


312         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

compounds,  which  resemble  most  natural  silicates  in  possessing  a 
comparatively  inert  chemical  nature,  and  which  suffer  but  slight 
decomposition  when  in  contact  with  water  or  are  scarcely  more 
than  appreciably  soluble  in  water.  This  hypothesis  receives 
further  confirmation  in  the  contention  of  R.  Gans15  that  artificial 
aluminum  silicates  behave  like  natural  zeolitic  silicates.  More- 
over, Way16  clearly  recognized  the  formation  of  such  compounds, 
and  Van  Bemmelen17  is  inclined  to  consider  the  absorbed  salts  as 
fixed  in  loosely  bound  chemical  combination. 

It  was  originally  considered  that  the  substitution  of  sodium  for 
calcium  and  magnesium  in  the  soil  was  a  potent  factor  in  bring- 
ing about  the  diffusion  of  the  salt-treated,  water-washed  soils. 
However,  this  first  conception  attributed  the  possible  effect  of 
the  chemical  exchange  to  the  double  decomposition  of  the  organic 
salts  of  calcium  and  magnesium  by  the  NaCl,  which  would  result 
in  the  formation  of  CaCl2  and  MgCl2  and  organic  compounds  of 
sodium.  Since  these  end-products  are  all  soluble  in  water,  a 
continuous  leaching  of  the  soil  with  that  solvent  would  be  likely 
to  deprive  the  soil  of  a  portion  of  its  organic  matter  and  of  a 
certain  amount  of  calcium  and  magnesium.  If  the  organic  matter 
herein  referred  to  can  be  properly  catalogued  under  those  elastic 
and  indefinite  terms,  humus  or  humates,  then  it  appears  reason- 
able in  the  light  of  Schloesing's  work18  to  expect  that  the  physical 
condition  of  the  soil,  depleted  of  such  organic  matter,  would  be 
seriously  affected  in  the  direction  already  suggested.  The  loss 
of  such  well-known  flocculating  agents  as  calcium  and  magnesium 
might  also  be  reflected  in  the  changed  physical  aspect  of  the 
soil. 

But  the  cogency  of  the  argument  just  presented  is  consider- 
ably lessened  by  the  results  of  the  experiment  to  be  described 
next.  Twenty-five  gram  portions  of  the  Davis  soil  were  subjected 
to  the  treatments  outlined  in  Table  VI.  The  soils  were  then 
allowed  to  dry,  after  which  10  grams  of  each  soil  were  sus- 
pended in  100  cc.  of  distilled  water  for  48  hours  before  the  sus- 


15  Cited  from  Exp.  Sta.  Kec,  vol.  31,  no.  1,  p.  22,  1914. 
ia  Journ.  R.  Agric.  Soc,  vol.  13,  p.  123,  1852. 
i7  Loc.  cit.;  also  in  Landw.  Vers.  Stat.,  vol.  35,  p.  121,  li 
is  Cited  from  Ililgard,  Soils  (1911),  p.  111. 


1916] 


Sharp:  Soluble  Salts  and  Soil  Colloids 


313 


TABLE  VI 

The  Effect  of  Eemoving  Humus  from  the  Soil  in  its  Relation 
Diffusion  Appearing  in  the  Soil  After  Salt  and 
Water  Treatments 


to  the 


No.  Soil 

1  25  grs.  (Davis  soil) 

2  25  grs.  (Davis  soil) 

4  25  grs.  (Davis  soil) 

5  25  grs.  (Davis  soil) 

6  25  grs.  (Davis  soil) 

7  25  grs.  (Davis  soil) 


Treatment 
Washed  with  H,,0 

50  cc.  4N  HC1  then  washed  with  H20 
HC1,*  H20,  NH4OH,  and  H20 
HC1,  H20,  NaCl,  and  H20 
HC1,  H20,  NH4OH,  H20,  NaCl,  and  H20 
NILOH 


Weight  of 

Suspended 

Matter 

from 

10  grams 

in  100  cc. 

of  water 

.0184 

.0118 

.0250 

.1216 

.1842 

.0176 


*  The  symbols  used  herein  designate  the  soil  treatments  on  the  filter  paper 
with  the  various  substances;  as  indicated,  H20  applications  were  generally  made 
between  applications  of  the  other  materials.  Solutions  approximating  normal 
strength  were  generally  employed. 


pension  above  the  deposited  material  was  drawn  off.  An  aliquot 
of  this  suspension  was  evaporated  to  dryness,  gently  ignited,  and 
weighed  to  obtain  the  data  of  column  4,  in  Table  VI. 

The  weight  of  the  suspended  matter  secured  from  suspensions 
of  Davis  soil  which  had  been  subjected  to  the  various  treatments 
gives  an  index  of  the  extent  of  the  physical  effects  of  such  treat- 
ments. The  treatment  with  II CI,  followed  by  washing  until  the 
nitrate  was  practically  free  from  chlorides,  seemed  to  reduce  the 
quantity  of  material  capable  of  being  held  in  suspension,  yet  the 
soil  had  no  doubt  lost  a  considerable  quantity  of  its  original 
calcium  and  magnesium  content.  This  fact  certainly  indicates 
that  the  loss  of  calcium  and  magnesium  from  the  soil  bears  but 
little  relation  to  the  diffusion  of  the  soils  as  a  general  proposition. 

The  soil  treatment  in  the  case  of  No.  4,  which  simulates  the 
procedure  generally  employed  in  humus  determinations,  with 
the  exception  that  water  is  used  as  a  final  application,  gives  a 
suspension  slightly  richer  in  solids  than  the  soil  treated  with 
water  alone.  If,  in  addition  to  the  treatment  just  mentioned, 
NaCl  is  then  added  to  the  humus  free  soil,19  the  suspension  be- 
comes a  very  turbid  liquid  rich  in  solids  in  a  highly  diffused  state, 


is  The  term  humus   here   signifies   that   portion   of   the   soil's   organic 
matter  removed  by  the  treatment  in  vogue  for  that  purpose. 


314        University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

as  shown  in  the  case  of  No.  6.  Evidently  the  loss  of  humus  and 
its  organic  colloids  increases,  rather  than  decreases,  the  amount 
of  material  finally  found  in  suspension,  for  No.  5,  receiving  HC1 
and  NaCl  treatment,  yields  a  suspension  containing  less  colloidal 
material  than  does  No.  6.  In  all  probability  the  increase  of 
colloidal  material  in  No.  6  over  No.  5  is  in  no  way  connected  with 
the  loss  of  organic  matter  of  No.  6,  but  is  more  likely  to  be  due 
to  the  conditions  and  treatments  involved  in  extracting  the 
humus.  Furthermore,  the  organic  colloids  of  soils  seem  to  have 
but  little  direct  relation  to  the  phenomena  which  appear  when 
certain  salts  are  washed  from  soils. 

That  the  deflocculated  condition  of  the  salt-treated  soils  might 
be  due  in  some  measure  to  the  loss  of  calcium  and  magnesium 
from  the  soil,  in  a  manner  somewhat  analogous  to  that  outlined 
by  Foerster,20  appeared  as  a  secondary  consideration.  The  actual 
loss  of  calcium  and  magnesium,  however,  cannot  be  considered 
the  sole  factor  in  producing  the  striking  conditions  observed. 
For,  if  that  were  the  case,  the  application  of  acids  followed  with 
washing  should  bring  about  similar  results.  On  this  point  War- 
ington  has  already  noted  that  normal  diffusion  of  the  colloids 
will  reappear  in  a  soil  which  has  once  been  flocculated  by  acids 
when  the  acids  and  such  salts  as  they  have  formed  are  removed 
by  washing.  Our  experience  with  soils  treated  in  the  manner 
just  described  fails  to  show  any  marked  increase  in  colloids,  as 
is  the  case  when  the  soil  is  treated  with  NaCl.  The  treatment 
with  HC1  followed  by  leaching  with  water  seems  to  retard  to  a 
notable  extent  the  rate  of  percolation  through  the  Davis  soil. 
However,  if  any  new  colloids  are  formed  by  this  treatment,  or  if 
the  original  colloidal  content  of  the  soil  is  thoroughly  diffused 
thereby,  as  the  case  may  be,  then  these  effects  are  entirely  oblit- 
erated by  the  subsequent  drying  of  the  soil,  for  a  suspension  of 
the  dry  soil  so  treated  yields  no  additional  colloidal  matter.  This 
fact  tends  to  confirm  the  view  that  the  loss  of  calcium  and  mag- 
nesium is  not  alone  responsible  for  the  diffusion  of  the  soils. 

Furthermore,  the  writer  has  shown  clearly  by  a  rather  simple 
procedure  that  a  considerable  exchange  or  a  direct  addition  of 
bases  is  essentia]  for  the  production  of  the  diffused  condition. 
20  Chem.  Ind.,  vol.  28,  no.  24,  p.  733,  1905. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  315 

A  solution  of  N/10  NaCl  was  allowed  to  act  upon  successive 
portions  of  Davis  soil  until  practically  no  more  calcium  or  mag- 
nesium was  taken  up  by  the  solution,  so  that  a  solution  of 
chlorides  was  formed  which  was  quite  inert  toward  this  soil.  A 
solution  secured  in  this  manner  appears  to  approach  the  satura- 
tion point  with  respect  to  calcium  and  magnesium  compounds 
of  the  soil.  This  solution  remained  practically  N/10  with  respect 
to  chlorine  throughout  its  successive  periods  of  contact  with  the 
soil,  and  at  no  time  was  the  solution  entirely  depleted  of  its 
sodium  content  by  the  interchange  with  calcium  and  magnesium. 
The  application  to  the  Davis  soil  of  a  solution  secured  in  the 
fashion  described  above  and  followed  by  washing  with  water  did 
not  result  in  such  pronounced  diffusion  as  was  observed  upon 
the  application  of  N/10  NaCl  solution  followed  bj'  washing  with 
water.  It  may  therefore  be  inferred  that  the  chemical  exchange 
of  bases  plays  a  significant  role  in  the  mechanism  by  which  dif- 
fusion is  produced  in  soils  which  have  been  washed  after  an 
addition  of  NaCl. 

By  the  various  lines  of  reasoning  outlined  above,  the  majority 
of  the  more  obvious  possible  causes  for  the  extreme  diffusion  of 
the  soils  under  discussion  have  been  completely  eliminated  or  at 
least  reduced  to  factors  of  little  significance.  For  this  reason, 
more  mature  thought  on  the  subject  has  directed  our  attention 
to  the  absorption  of  sodium,  which  has  been  previously  men- 
tioned, as  the  keynote  to  the  deteriorated  physical  condition  of 
the  salt-treated,  water-washed  soils.  The  substitution  of  sodium 
for  the  calcium,  magnesium,  or  other  bases  in  the  silicate  complex, 
or  the  direct  addition  of  sodium  to  such  a  complex,  results,  ac- 
cording to  our  proposed  hypothesis,  in  the  formation  of  new 
jelly-like  colloids,  capable  of  becoming  highly  diffused  when  in 
contact  with  water.  The  fact  that  leaching  Na2C03,  NaOH, 
NaHC03,  NaCl,  Na2S04,  and  NaN03  from  the  soil  brings  about 
the  same  appearance  of  the  soil  and  the  same  physical  manifesta- 
tions of  deflocculation,  becomes  more  comprehensible  if  the  view 
is  accepted  that  the  absorption  of  sodium  and  the  new  compounds 
formed  thereby  are,  in  the  main,  the  factors  responsible  for  the 
deflocculated  condition  of  the  soils  so  treated.  Moreover,  these 
various  treatments  are  accompanied  by  the  appearance  of  widely 


316         University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

different  quantities  of  calcium  and  magnesium  in  the  percolate, 
thus  affording  additional  evidence  that  the  increased  solubility 
and  the  consequent  loss  of  these  elements  from  the  treated  soils 
is  not  the  prime  factor  in  causing  the  ultimate  diffusion  of  the 
soil  colloids.  The  facts  herein  presented  concerning  the  absorp- 
tion of  sodium  and  the  formation  of  new  colloidal  substances  cor- 
responds in  the  main  with  the  idea  of  unsaturated  silicates  and 
absorption  phenomena,  as  developed  by  Cameron,21  Harris,22  and 
Loew,23  and  others,  in  their  work  dealing  with  acid  soils. 

The  conception  of  the  causes  of  the  apparent  deflocculation, 
as  discussed  above,  receives  tangible  substantiation  in  the  results 
of  the  following  experiment.  Twenty  grams  of  Davis  soil  were 
subjected  to  the  treatments  outlined  in  Table  VII.  After  wash- 
ing with  water,  the  soils  were  dried  at  room  temperature  and 
then  10  grams  of  each  were  suspended  in  100  cc.  of  water  to 
secure  the  figures  in  the  last  column.  Meanwhile  the  calcium 
and  magnesium  in  the  total  percolates  were  determined,  in  the 
usual  fashion. 


TABLE  VII 

Effects  of  Washing  Various  Sodium  Salts  from  the  Davis  Soil 


Soil 
No.  (Davis)  Treatments 

1  20  grs.         H,0  only 

2  20  grs.         100  cc    N/10    NaOH    fol- 

lowed with  water 

3  20  grs.         100  cc  N/10  Na2  CO,  fol- 

lowed with  water 

4  20  grs.         100  cc.    N/10    NaCl    fol- 

lowed with  water 

5  20  grs.         100  cc.     (approx.)     N/10 

NaHC03  followed  with 
water 
10         20  grs.         100  cc.  N/10  NaNOy  fol- 
lowed with  water 


Calcium 
in  Total 
Percolate 

Magnesium 
in  Total 
Percolate 

Weight  of 
Suspended 
Matter 
from  10 
grams  in 
100  cc.  of 

grs. 
.0017 

grs. 
.0014 

water 
.0348 

.0015 

.0005 

.4860 

.0020 

.0037 

.6500 

.0108 

.0109 

.4720 

.0035 

.0086 

.4880 

.0088 

.0103 

.4340 

It  is  clear  that  all  of  the  sodium  salts  used  in  the  above  ex- 
periment produce  approximately  the  same  effects  on  the  colloidal 
matter  of  the  soil  when  washed  from  it,   as  indicated  by   the 


^i  The  Soil  Solution   (Chemical  Publishing  Co.),  1911. 
22  Journ.    Phys.    Chem.,    vol.    28,    no.    4,    p.    355 ;    and    Michigan    Agric. 
Exper.  Sta.  Tech.  Bull.  19. 

28  Porto  Rico  Agric.  Exper.  Sta.,  Bull.  13,  1913. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  317 

amount  of  material  finally  found  in  suspension.  All  of  the 
salt-and-water  treatments  yielded  suspensions  containing  more 
than  ten  times  the  suspended  matter  found  in  the  water-washed 
soil.  From  the  evidence  reported  in  the  above  table  it  seems 
proper  to  infer  that  neither  the  nature  of  the  added  sodium  salt, 
nor  the  loss  of  calcium  and  magnesium  from  the  soil,  have  much 
part  in  the  production  of  the  deflocculated  condition  noted  in  the 
salt-treated,  water-washed  soils.  The  data  of  Table  VII  are  also 
discussed  later  in  their  relation  to  the  possible  effects  of  NaOH 
and  the  OH-ion  on  the  physical  condition  of  soils. 

The  interchange  of  ions  between  the  soil  silicates  and  neutral 
salt  solutions  like  NaCl  or  Na2S04,  which  seems  to  result  in  the 
formation  of  new  colloidal  substances,  also  necessitates  the  simul- 
taneous presence  of  free  acid  or  of  new  salts  of  the  free  acid  as 
the  calcium  or  magnesium  salts,  in  the  solution  bathing  the  soil 
particles.  As  previously  discussed,  both  of  these  conditions  have 
been  encountered  in  the  supernatant  liquid  of  a  neutral  salt 
solution  in  contact  with  soil  and  also  in  the  first  portion  of  the 
percolate  coming  through  a  soil  to  which  a  neutral  salt  has  been 
added.  The  constant  presence  of  the  free  acid  and  its  soluble 
salts,  together  with  more  or  less  of  the  salt  originally  added,  oc- 
casions the  maintenance  of  a  flocculated  condition  of  the  soil 
colloids,  so  that  any  additional  colloidal  matter  which  may  have 
been  produced  is  not  sufficiently  effective  on  the  physical  char- 
acter of  the  soil  to  be  easily  recognized. 

If  it  be  assumed  that  new  and  additional  colloidal  material 
is  formed  in  the  soil  by  virtue  of  the  salt-and-water  treatments, 
then  it  is  most  likely  in  existence  prior  to  the  washing  process,  but 
its  effects  on  the  physical  condition  of  the  soil  are  not  manifested 
until  the  surrounding  medium  has  become  sufficiently  dilute,  with 
respect  to  salts,  to  allow  of  a  more  or  less  complete  diffusion  of  the 
soil  colloids.  The  addition  of  the  neutral  salts  either  produces 
new  colloidal  matter  simultaneously  with  the  chemical  inter- 
change of  bases,  which  occurs  independently  of  the  wrashing  with 
water,  or  in  some  manner  disintegrates  the  existing  colloidal 
aggregates.  The  former  seems  the  more  plausible,  especially  in 
view  of  certain  phases  of  the  work  herein  presented.  In  addition 
we  also  have  evidence  that  the  washing  with  water  alone  does  not 


318         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

measureably  increase  the  colloidal  content  of  the  soil,  nor  does 
it  materially  affect  its  physical  condition. 

At  least  one  interpretation  of  these  facts  seems  plausible, 
namely,  that  the  neutral  salts  or  their  ions  function  as  the  creative 
agent  whereby  diffusible  colloidal  matter  is  formed,  while  the 
washing  with  water  serves  in  the  entirely  separate  capacity  of 
removing  from  the  sphere  of  activity  any  flocculating  agents  in 
the  shape  of  soluble  salts  which  may  have  been  present. 

Certain  modifications  of  the  hypothesis  just  presented  must  be 
considered  in  order  to  account  for  the  action  on  soils  of  the  salts 
which  give  an  alkaline  reaction.  First  of  all,  the  chemical  pro- 
ducts that  can  possibly  be  formed  when  the  latter  class  of  salts 
is  allowed  to  act  upon  soils  are  on  the  whole  comparatively  in- 
soluble and  hence  possess  relatively  small  flocculating  powers. 
Owing  to  this  fact  the  washing  process,  which  seems  to  be  essen- 
tial for  the  appearance  of  the  diffusion  in  soils  treated  with 
neutral  salts,  is  not  such  an  important  factor  in  case  of  soils 
treated  with  salts  giving  rise  to  an  alkaline  reaction. 

Instead  of  attributing  the  deflocculation  of  soils  which  have 
received  NaOH  or  alkaline  carbonates,  wholly  to  the  OH-ion 
content  of  the  solution  or  to  the  alkaline  reaction  so  produced, 
our  present  theory,  supported  by  the  facts  already  presented, 
proposes  to  account  for  the  diffusion  of  the  soils  so  treated  by  the 
formation  of  colloidal  sodium  alumino-silicate  complexes  under 
conditions  which  permit  of  an  immediate  deflocculation.  Therein 
lies  the  difference  in  the  behavior  of  neutral  salts  on  soils,  as 
compared  with  that  of  salts  of  an  alkaline  reaction.  In  all  prob- 
ability somewhat  similar  compounds  are  formed  in  the  two  cases, 
but  in  the  first  case,  with  the  exception  of  certain  circumstances, 
the  conditions  are  such  as  to  prevent  deflocculation,  while  in  the 
second  case  deflocculation  is  at  least  permitted  and  perhaps 
accentuated. 

A  Possible  Relation  Between  the  Composition  of  the  Soil 

Solution  and  the  Diffusion  Phenomena  in  Certain 

Salt-Treated,  Water-Washed  Soils 

The  first  two  hypotheses  formulated  to  explain  the  diffused 

condition  of  the  salt-treated  soils  dealt  largely  with  the  soil  itself 

and  with  the  absorption  of  sodium  by  the  soil.    A  third  hypothesis 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  319 

proposes  to  attribute  the  diffusion  of  the  soil  colloids  to  changes 
in  the  composition  of  the  medium,  namely  the  soil  solution.  Such 
a  diffused  condition  of  the  soil  colloids  might  be  brought  about 
by  an  increase  in  the  OH-ion  content  of  the  solution  bathing  the 
soil  particles.  This  concept  is  based  on  the  fact  that  clay  is  a 
negatively  charged  colloid,  and  according  to  the  views  now  held 
the  further  addition  of  negative  ions  to  such  a  colloidal  suspension 
causes  these  particles  to  assume  greater  charges  of  like  sign,  so 
that  they  repel  each  other  and  thus  remain  distributed  through- 
out the  medium  in  a  stabilized  condition.  On  the  other  hand,  it 
is  held  that  the  introduction  of  ions  bearing  an  opposite  charge 
to  that  of  the  colloidal  particles  neutralizes  the  charge  associated 
with  the  particles,  so  that  they  no  longer  repel  each  other  but 
gather  together  in  aggregates  or  noccules.  For  a  more  complete 
discussion  and  bibliography  dealing  with  these  phenomena,  the 
reader  is  referred  to  the  work  of  Whitney  and  Ober.24  In  a  more 
recent  review  Tolman25  has  advanced  a  clear  conception  of  colloids 
and  their  behavior,  which  affords  us  a  satisfactory  working  basis 
for  studies  on  these  substances.  According  to  this  author,  the 
surface  tension  existing  between  the  particles  and  the  surround- 
ing liquid  is  the  factor  which  determines  the  degree  of  dispersion 
of  the  particles  in  the  liquid.  Thus  systems  of  zero  surface  tension 
are  at  equilibrium.  Those  possessing  a  negative  surface  tension 
increase,  automatically,  their  degree  of  dispersion  until  the  zero 
value  is  reached,  while  those  of  positive  surface  tension  tend  to 
become  less  dispersed.  Since  the  surface  tension  referred  to  is 
the  resultant  of  many  forces,  it  may  be  readily  affected  in  numer- 
ous wTays,  as  by  the  mechanical  process  of  grinding,  by  heating,  by 
the  addition  of  electrolytes,  or  by  the  passage  of  an  electric  cur- 
rent. Through  the  application  of  these  considerations  we  may  be 
able  to  decipher  more  clearly  and  definitely  the  problems  involved 
in  the  effects  of  salts  on  the  physical  condition  of  soils. 

It  is  possible  that  deflocculants  other  than  the  OH-ion  may 
have  been  introduced  into  the  soil  solution  by  means  of  the  salt- 
and- water  treatments,  but  the  latter  factor  obviously  appears  as 
the  most  significant   deflocculating  agent  likely   to   be   present 


24  Journ.  Amer.  Chem.  Soc,  vol.  23,  p.  842,  1901. 

25  Journ.  Amer.  Chem.  Soc,  vol.  35,  no.  4,  1913. 


320         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

under  the  conditions  of  the  experiments  and  hence  merits  first 
attention.  Probably  the  most  striking  evidence  of  the  possibility 
that  the  OH-ions  in  the  soil  solution  may  be  justly  deemed  the 
cause  of  the  diffusion  of  the  soils  with  which  this  paper  is  chiefly 
concerned,  lies  in  the  well-known  deflocculating  effect  of  dilute 
solutions  of  NaOH  on  the  soil  colloids.  Thus  the  poor  tilth  and 
cultivating  qualities  of  lands  impregnated  with  black  alkali 
(Na,C03)  has  been  rather  vaguely  attributed  to  the  OH-ions 
derived  from  the  hydrolysis  of  the  Na2C03.  This  expression  fails 
to  offer  any  explanation  of  the  mechanism  whereby  the  OIT-ion 
induces  the  observed  effects,  neither  does  it  allow  of  any  possible 
effect  of  the  Na-ion  on  the  physical  properties  of  the  soil.  How- 
ever, if  our  interpretations  be  not  too  far  amiss,  there  are  several 
reasons,  not  based  on  theoretical  considerations  alone,  but  sub- 
stantiated by  facts,  for  suspecting  that  the  OH-ion  is  of  much 
smaller  significance  than  the  accompanying  Na  or  other  basic  ion 
in  the  final  effect  of  the  chemical  compound  on  the  physical  condi- 
tion of  the  soil. 

The  common  conception  that  substances  which  yield  an  alka- 
line reaction  on  hydrolysis  occasion  the  deflocculation  of  the  soil 
colloids  is  frequently  accepted  without  qualification,  even  by 
those  working  with  alkali  soils,  notwithstanding  some  facts  now 
extant  which  deny  its  validity.  Thus,  as  early  as  1874  Durham20 
pointed  out  that  clay  suspensions  cleared  more  rapidly  in  strong 
Na2C03  solutions  than  in  distilled  water.  Whitney  and  Straw27 
have  also  shown  that  NaOH  in  dilute  solutions  tends  to  stabilize 
suspensions  of  colloidal  silver,  china  clay,  and  lampblack,  and 
that  emulsions  of  turpentine,  carvene,  and  carvol  are  also  acted 
upon  in  a  similar  manner.  The  behavior  of  these  substances  also 
gave  evidence  that  the  maximum  stability  occurred  at  certain 
concentrations  of  NaOH,  above  which  flocculation  was  produced 
and  below  which  the  effect  of  the  NaOH  was  not  so  pronounced. 
The  investigations  of  Hall  and  Morison  already  referred  to  sub- 
stantiate, in  the  main,  the  previous  citations  on  the  point  under 
discussion.     Quite  recently  Maschhaupt28  has  found  that  even 


26  Chern.  News,  vol.  30,  no.  676,  p.  57,  1874. 

27  Journ.  Amer.  Chem.  Soc,  vol.  29,  p.  325,  1907. 

28  Landw.  Vers.  Stat.,  vol.  83,  p.  467,  1914. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  321 

0.015  N  NaOH  has  a  flocculating  effect  on  the  colloidal  matter 
of  a  sandy  loam  soil,  while  more  dilute  solutions  of  NaOII  stabil- 
ized the  diffusible  colloidal  matter.  He  further  asserts  that  alkali 
carbonates  act  much  in  the  same  manner.  Despite  the  preceding 
evidence,  Rohland29  still  contends  that  the  flocculation  of  clay 
soils  by  lime  is  due  to  the  OH-ion. 

While  working  along  similar  lines,  the  author  has  noted  that 
a  suspension  of  the  Davis  clay  loam  settles  out  more  rapidly  in 
a  0.05  N  solution  of  NaOII  than  in  distilled  water,  but  that  solu- 
tions of  greater  dilution  were  stabilizing  in  their  effects.  On  the 
other  hand,  no  solution  of  Na2C0330  proved  effective  as  a  stabiliz- 
ing agent  as  compared  with  distilled  water,  while  solutions  of 
Na2COa  stronger  than  0.022  N  had  a  decided  flocculating  effect. 
This  difference  in  the  behavior  of  NaOH  and  Na2C03  has  not  come 
to  the  writer's  attention  before  in  the  literature  of  the  subject, 
and  fails  to  support  the  widespread  teaching  that  Na2C03  and 
salts  which  hydrolize  similarly  deflocculate  the  soil  colloids 
through  the  agency  of  the  OH-ion.  But  the  most  striking  fea- 
ture of  the  action  of  NaOH  on  the  soil  suspension  was  the  marked 
resemblance  of  the  soils  suspended  in  that  medium  to  the 
NaCl  +  H20  soil  suspended  in  distilled  water.  The  yield  of 
suspended  matter  from  these  two  suspensions  proved  to  be  of 
about  the  same  magnitude,  as  shown  in  Table  II.  A  cursory  con- 
sideration of  this  fact  obviously  supports  the  contention  that  the 
OH-ion  content,  or  the  alkalinity  of  the  suspending  solution,  may 
be  responsible  for  the  diffusion  of  the  soil  colloids  in  the  cases 
under  consideration.  However,  an  interesting  point  to  the  con- 
trary lies  in  the  fact  that  suspensions  of  the  Davis  soil  in  very 
dilute  solutions  of  NaOH  can  not  be  distinguished  from  sus- 
pensions of  the  same  soil  in  distilled  water.  That  is  to  say,  NaOH 
solutions  of  a  concentration  of  N/1500  to  N/2000  exercised  no 
recognizable  effect  on  the  soil  colloids.  The  concentrations  here 
referred  to  approach  the  same  order  of  alkalinity  as  that  found 
in  the  solution  bathing  the  particles  of  the  highly  diffused 
NaCl  -f-  H20  soil.    Evidently  some  other  factor  than  the  OH-ion 


29  Landw.  Jahrb.,  vol.  44,  no.  3,  p.  437,  1913;  and  Landw.  Vers.  Stat., 
vol.  85,  nos.  1-2,  p.  123,  1914. 

so  Baker's  analyzed  Na2C03  was  used  in  these  experiments  except  where 
otherwise  noted. 


322         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

content  of  the  solution  is  either  responsible  for  the  diffused  con- 
dition of  the  soil  colloids,  or  at  least  is  of  material  assistance  in 
producing  this  effect. 

Moreover,  it  has  been  demonstrated  that  the  washing  out  of 
the  excess  NaOH  does  not  materially  benefit  the  injured  physical 
condition  of  the  soil,  although  the  alkalinity  of  the  soil  solution 
was  thereby  reduced  to  a  concentration  comparable  with  that  of 
the  dilute  solutions  to  which  reference  has  just  been  made. 
Actual  determinations  of  the  alkalinity  of  the  final  portions  of 
the  percolate  from  soils  to  which  NaOH  has  been  added  show 
only  such  alkalinity  as  the  percolate  from  the  normal  soil.  If 
we  accept  the  view  brought  forth  by  Cameron,31  which  seems 
justifiable,  then  the  percolates  from  these  soils  approach,  as  a 
limit,  the  chemical  composition  of  the  soil  solution  and  hence 
we  may  conclude  that  the  alkalinity  of  the  soil  solution  is  of  the 
same  order  of  magnitude  as  that  of  the  percolate.  The  fact  that 
washing  the  NaOH  from  the  soil  is  not  accompanied  by  an  im- 
provement in  the  physical  condition  of  the  soil  may  be  fairly 
interpreted  as  substantially  affirming  the  view  that  the  OH-ion 
is  of  little  moment  in  the  diffusion  of  the  NaCl  -|-  H20  soil,  and 
possibly  has  but  little  connection  with  the  deflocculation  of  soils 
to  which  NaOH  has  been  added.  Furthermore,  the  facts  just 
discussed,  taken  in  conjunction  with  those  considered  under  the 
heading  of  sodium  absorption,  lend  an  appearance  of  reality  to 
the  assumption  that  the  sodium,  even  in  the  case  of  direct  addi- 
tion of  NaOH  to  soils,  is  the  principal  agent  in  creating  the 
diffused  condition  in  soils  so  treated. 

Moreover,  the  writer  has  found  that  NaHC03,  Na2C03,  and 
NaOH  have  distinctive  effects  on  the  soil  colloids.  In  higher 
concentrations  all  three  salts  prove  to  be  flocculants ;  in  very  weak 
concentrations,  as  of  the  order  of  N/2000  or  less,  they  seem  to 
resemble  distilled  water  in  their  behavior  toward  the  soil  col- 
loids. In  medium  concentrations,  that  is,  those  less  than  0.05 
N,  NaOH  is  a  deflocculating  agent,  Na2C03  acts  much  like  dis- 
tilled water,  while  NaHC03  seems  to  be  a  pronounced  flocculant. 
At  least  the  NaOH  and  Na2C03  yield  a  certain  amount  of 
OH-ions,  and  in  the  wide  range  of  concentrations  employed  some 

3i  Eighth  Intern.  Cong.  Appl.  Chem.,  vol.  15-16,  p.  49,  1912. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  323 

point  must  have  been  encountered  at  which  the  Oil-ion  concen- 
tration of  these  two  was  the  same  or  approximately  so.  Yet  the 
two  salts  exercised  a  different  influence  on  the  soil  colloids  at  all 
the  concentrations  used,  with  the  exception  of  the  highest  and 
lowest  concentrations.  This  fact  indicates  that  some  other  factor 
than  the  OH-ion  is  effective  in  determining  the  degree  of  dis- 
persion of  the  soil  colloids.  What  application  this  may  have  to 
black  alkali  lands  is  a  question,  for  under  natural  conditions  it  is 
most  likely  that  all  three  compounds,  NaOH,  NaHC03,  and 
Na2C03,  and  their  respective  ions  occur. 

But  the  most  striking  feature  of  this  phase  of  the  problem 
lies  in  the  fact  that  the  washing  out  of  the  soluble  matter  from 
separate  portions  of  the  Davis  soil  receiving  NaOH,  Na2C03,  and 
NaHC02  results  in  the  same  way.  The  soil  becomes  very  im- 
pervious and  diffuses  when  shaken  with  distilled  water.  Thus 
the  cylinder  soils  receiving  Na2C03  have  been  exposed  to  condi- 
tions permitting  the  leaching  out  of  the  soluble  salts,  at  least 
from  the  surface  soil,  so  that  they  now  exhibit  the  same  peculiari- 
ties as  the  soils  treated  analogously  in  the  laboratory. 

The  systems  so  far  considered  have  been  largely  made  up  of 
soils  to  which  various  quantities  of  NaOH,  Na2C03  or  NaHC03 
have  been  added.  To  ascertain  to  what  extent  the  facts  so  gained 
are  applicable  to  the  conditions  existing  in  the  laboratory  sam- 
ples of  NaCl  -f-  H20  soil  or  to  those  of  the  field  cylinder  soils 
receiving  NaCl  and  Na2S04,  necessitates  the  measurement  of  the 
alkalinity  obtaining  in  these  soils.  We  have  attempted  to  secure 
some  information  with  regard  to  the  quantity  of  OH-ions  or  the 
alkalinity  in  the  solution  containing  a  suspension  of  the 
NaCl  -f-  H20  soil,  but  the  persistent  color  of  this  solution  has 
made  it  impracticable  to  employ  it  directly  with  the  various  indi- 
cators. It  would  seem,  however,  from  actual  titrations  made  in 
the  usual  manner  using  methyl  orange  as  the  indicator,  that  the 
alkalinity  of  the  soils  in  the  cylinders  receiving  NaCl  and  Na2S04 
had  been  somewhat  increased  over  that  of  the  control  soils.  But 
solutions  secured  from  soils  treated  in  the  laboratory  in  a  manner 
similar  to  the  treatment  of  the  field  soils  failed  to  verify  con- 
sistently the  above  observations.  At  the  present  time  we  are  en- 
gaged in  a  study  of  the  reaction  of  the  soil  suspensions  by  the  use 


324         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

of  the  hydrogen  electrode.  The  results  thus  far  secured  indicate 
that  there  is  not  a  sufficient  quantity  of  OH-ions  in  the  NaCl  + 
H20  soil  to  produce  the  degree  of  deflocculation  observed  therein. 

If  the  OH-ion  content  of  the  medium  is  assumed  to  be  the 
causal  agent  for  the  diffusion  of  the  soil  colloids,  it  would  appear 
an  equally  plausible  assumption  that  the  transference  of  the  sus- 
pending medium  from  a  diffused  soil  to  the  original  untreated 
soil  would  carry  with  it  the  deflocculating  agent,  so  that  the 
second  soil  would  register  to  some  degree  the  physical  manifesta- 
tions of  deflocculation.  To  test  the  correctness  of  this  hypothesis 
the  following  experiment  was  undertaken.  Twenty-five  grams  of 
NaCl  +  H20  soil  were  suspended  in  250  cc.  of  water.  The  col- 
loidal matter  of  such  a  suspension  normally  remains  in  a  stabil- 
ized condition  for  at  least  three  or  more  weeks,  when  exposed  to 
laboratory  conditions.  This  suspension  was  cleared,  however,  at 
the  expiration  of  48  hours  by  passing  it  through  the  Pasteur 
Chamberland  filtering  candle  under  pressure.  This  was  accom- 
plished with  considerable  care  so  as  to  conform  to  the  conditions 
found  by  Briggs32  to  yield  the  most  satisfactory  results.  The 
solution  secured  in  the  manner  described  from  the  NaCl  -f-  H20 
soil  was  then  used  as  a  suspending  medium  for  10  grams  of  un- 
treated Davis  soil.  A  comparison  of  the  suspension  thus  formed 
with  a  suspension  of  the  same  soil  in  distilled  water  disclosed  no 
recognizable  difference.  Thus  it  would  appear  that  a  transference 
of  the  suspending  medium  of  a  diffused  NaCl  -f-  H20  soil  to  a 
second  untreated  soil  does  not  carry  with  it  the  agent  causing  the 
deflocculation  of  the  first  soil.  Hence,  any  hypothesis  ascribing 
the  altered  physical  condition  of  the  NaCl  +  H20  soil  to  changes 
in  the  soil  solution  seems  untenable. 

The  value  of  the  results  secured  by  the  procedure  outlined 
above  may  be  open  to  question.  To  avoid  such  criticism,  the 
writer  made  the  following  experiment,  which  distinctly  shows 
that  the  transference  of  a  soluble  soil  deflocculant  from  one  soil 
to  another  by  the  method  employed  is  susceptible  of  proof.  A 
N/50  NaOH  solution  in  contact  with  the  Davis  soil  tends  to 
maintain  the  soil  colloids  in  a  stabilized  condition.  Such  a  dif- 
fused suspension  was  subjected  to  the  filtering  treatment  out- 

82  U.  S.  Dept.  Agr.,  Bur.  of  Soils,  Bull.  19,  p.  31,  1902. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  325 

lined  above  and  on  passing  through  the  Pasteur  filter  yielded  a 
clarified  solution  which  had  not  lost  its  power  to  deflocculate  the 
Davis  soil.  The  writer  is  fully  aware  that  conditions  might  arise 
wherein  such  treatments  would  considerably  modify  the  defloc- 
culating  power  of  the  solute — for  example,  in  case  of  very  dilute 
solutions  where  absorption  by  the  soil  and  filter  would  be  rela- 
tively large  and  possibly  of  sufficient  magnitude  to  markedly 
diminish  the  quantity  of  deflocculant  in  the  filtrate,  which  would 
result  undoubtedly  in  a  decrease  in  the  deflocculating  power  of 
the  solution.  A  similar  reduction  in  deflocculating  power  of  a 
solution  would  also  be  likely  to  appear  if  a  solution  were  sub- 
jected to  repetitions  of  the  procedure  described  above. 

Despite  the  evidence  above  some  doubt  may  still  be  enter- 
tained as  to  the  absence  of  significant  quantities  of  OH-ions  in 
the  films  of  water  on  the  immediate  surfaces  of  the  colloidal 
particles,  especially  in  view  of  the  probability  that  the  colloidal 
matter  in  the  diffused  soils  consists  largely  of  compounds  of  the 
chemical  nature  of  sodium  silicate,  which  hydrolizes  to  some 
extent  in  water  and  eventually  gives  rise  to  OH-ions,  thereby 
lowering  the  surface  tension  as  described  by  Tolman33  and  like- 
wise producing  the  conditions  obtaining  in  the  "natant"  col- 
loids of  Hall  and  Morison.34  Moreover,  the  results  secured  by 
Briggs35  on  the  absorption  of  alkali  hydrates  by  silica  tends  to 
confirm  the  proposed  conception  of  "natant"  colloids.  If  this 
be  the  case,  the  rate  of  diffusion  of  these  ions  from  the  films  into 
the  more  dilute  medium  would  be  the  factor  determining  whether 
it  would  be  possible  to  transfer  a  sufficient  quantity  of  these 
ions,  by  means  of  the  solution,  to  be  effective  on  the  physical 
condition  of  a  second,  otherwise  untreated,  soil.  Under  the  condi- 
tions of  the  experiment  just  cited,  a  contact  period  of  two  days 
was  allowed  for  such  diffusion,  which  would  appear  to  allow 
ample  time  therefor. 

Furthermore,  as  observed  by  Whitney  and  Straw36  and  others, 
the  fact  that  NaOH  in  certain  concentrations  tends  to  stabilize 


33  Loc.  cit. 

3-t  Loc.  cit. 

35  Joum.  Phys.  Chem.,  vol.  9,  p.  617,  1905. 

se  Loc.  cit. 


326         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

colloidal  matter  of  a  comparatively  inert  chemical  nature  forms 
the  basis  of  an  argument  which  opposes  the  conceptions  herein 
presented,  and  which  favors  the  view  that  the  OH-ion  may,  after 
all,  play  an  important  role  in  the  diffusion  of  colloids.  Thus, 
systems  composed  of  colloidal  silver,  lampblack,  or  relatively 
pure  organic  substances  in  contact  with  NaOH  probably  do  not 
offer  opportunity  for  the  direct  addition  of  the  sodium  or  the 
exchange  of  ions  whereby  sodium  is  taken  up,  a  factor  which 
forms  an  essential  link  in  the  scheme  proposed  by  the  writer  to 
explain  the  effects  of  the  alkali  salts  on  soils.  Also  the  experi- 
ments of  Bliss,  cited  by  Whitney  and  Straw,37  give  an  indica- 
tion that  NaOH  may  be  an  effective  agent,  through  the  medium 
of  the  OH-ion.  No  attempt  is  made,  however,  to  deny  the  com- 
plete ineffectiveness  of  the  OH-ion,  for  it  undoubtedly  has  an 
important  influence  on  the  physical  condition  of  colloids,  as  is 
the  case  with  many  ions.  But  with  regard  to  the  physical  condi- 
tion of  the  salt -treated  Davis  soil,  it  is  very  evident  that  the 
OH-ion  is  a  factor  of  much  less  significance  than  the  other  ions 
associated  with  it. 

The  Precipitating  Effect  of  Various  Acids  and  Salts 
on  the  Soil  Colloids 

There  seemed  some  possibility  that  the  presence  of  some  ion 
or  ions,  other  than  the  OH-ion,  in  the  soil  solution  might  be  held 
accountable  for  the  extreme  diffusion  of  the  NaCl  -(-  H20  soil 
and  soils  similarly  affected  by  other  salt  treatments.  Conse- 
quently an  extensive  series  of  test-tube  experiments  dealing  with 
the  effects  of  various  acids  and  salts  on  the  soil  suspension  were 
undertaken.  The  results  of  these  tests  are  briefly  referred  to  at 
this  time  in  their  relation  to  the  condition  existing  in  the  salt- 
treated,  water-washed  soils. 

It  was  found  that  N/2000  HC1  and  H2S04  perceptibly  floccu- 
lated the  soil  colloids,  as  compared  with  distilled  water  sus- 
pensions of  the  same  soil.  To  attribute  this  action  wholly  to  the 
II-ion  of  the  acid  would,  in  the  writer's  opinion,  be  erroneous, 
for  no  doubt,  salts  are  immediately  formed  when  the  acid  comes 


■■<  hoc.  cit. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  327 

into  contact  with  the  soil.  Nevertheless,  it  is  significant  that 
acids  of  the  low  concentration  here  employed  are  more  efficient 
flocculants  than  their  salt  solutions  of  similar  concentrations. 
Hence  the  nnneutralized  acid  in  very  dilute  concentrations  un- 
doubtedly exercises  a  pronounced  flocculating  power,  so  that  this 
factor  is  eliminated  as  the  possible  deflocculant  in  the  case  of 
NaCl  +  H20  soil. 

Solutions  of  the  chlorides,  sulphates,  and  bicarbonates  of 
calcium,  sodium,  ammonium,  and  potassium,  were  also  studied 
with  regard  to  their  effects  on  the  colloidal  matter  of  soils.  These 
salts  in  solutions  ranging  in  concentration  from  N/1500  to  N/500 
possessed  distinct  flocculating  powers.  Solutions  of  higher  con- 
centrations were  likewise  flocculating  in  their  effect,  while  more 
dilute  solutions  behaved  similarly  to  distilled  water.  Hence  the 
diffused  condition  of  the  NaCl  +  H20  soil  cannot  be  attributed 
to  the  mere  dilution  of  the  neutral  sodium  salts  or  of  the  simple 
salts  formed  by  reactions  between  the  added  salts  and  the  soil 
silicates.  As  previously  indicated,  this  statement  must  not  be 
construed  to  include  the  systems  soil  +  NaOH,  or  soil  +  Na2C03, 
but  must  be  considerably  modified  to  express  the  facts  existing 
in  those  cases. 

The  Effects  of  Washing  Various  Salts  from  the 
Soil  with  Water 

The  washing  out  of  KC1  and  NH4C1  from  the  Davis  soil  with 
water  gave  essentially  the  same  results  as  accompanied  the  re- 
moval of  the  sodium  salts  by  the  same  means.  On  the  other 
hand,  the  leaching  out  of  calcium  salts  seemed  to  leave  the  soil 
colloids  in  a  more  flocculated  condition  than  in  the  normal,  un- 
treated soil,  though  this  effect  was  by  no  means  so  pronounced 
as  when  the  calcium  salts  were  allowed  to  remain  in  contact  with 
the  soil  particles.  According  to  the  ideas  herein  presented,  the 
effect  of  a  salt  solution,  either  while  in  contact  with  the  solid 
particles  or  after  its  removal  from  the  soil  by  washing  with  dis- 
tilled water,  upon  the  physical  condition  of  soils  or  complex 
silicates  of  such  a  character  as  to  admit  of  chemical  exchange  of 
ions,  is,  in  a  measure,  dependent  upon  the  nature  of  the  chemical 


328         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

bodies  formed  by  virtue  of  this  interchange  of  ions.  The  soluble 
products,  including  the  salts  of  calcium,  magnesium  or  other 
bases,  which  are  formed  when  salt  solutions  are  allowed  to  act 
upon  soils,  must  be  considered,  if  a  true  conception  of  the  physi- 
cal effects  of  the  added  salts  is  to  be  secured.  In  addition,  the 
individual  properties  of  the  new  silicate  complex,  which  is 
formed  simultaneously  with  the  exchange  of  ions,  must  be  recog- 
nized as  bearing  significantly  on  the  final  effects  of  the  added 
salt  on  the  physical  condition  of  the  soil.  Undoubtedly,  these 
factors  have  a  bearing  on  the  effects  of  salts  on  the  capillary 
movement  of  water  in  soils,  and  make  impossible  the  direct  appli- 
cation of  physical  laws  concerning  surface  tension  and  densities 
to  the  phenomena  of  capillary  rise,  as  Briggs  and  Lapham38  have 
attempted.  Instead,  the  factors  discussed  above  may  help  to 
harmonize  the  observations  made  by  these  investigators  with  the 
more  recent  findings  of  Kossovich.39 

The  addition  to  soils  of  KC1,  NH4C1,  NaN03,  Na2S04  or  NaCl, 
and  in  fact  most  neutral  salts,  has  been  shown  by  Way,40  Eich- 
horn,41  Henneberg  and  Stohman,42  Peters,43  Van  Bemmelen,44 
Bradley,45  Curry  and  Smith,46  and  others,  to  result  in  increasing 
the  quantity  of  calcium,  magnesium  and  other  metallic  ions  in  the 
solution  secured  from  soils  so  treated,  as  compared  with  the  same 
soils  receiving  distilled  water.  Furthermore  it  has  been  shown 
by  Hall  and  Morison,47  Davis,48  Patten  and  Gallagher,49  Masoni,50 
and  others  that  calcium  and  magnesium  salts  possess  more  pro- 
nounced flocculating  powers  than  the  corresponding  salts  of  the 
alkali  metals.     This  fact  may  account  for  the  different  rates  at 


1912 


ss  U.  S.  Dept.  Agric,  Bur.  of  Soils,  Bull.  19,  1902. 
so  Cited  from  Exp.  Sta.  Eec,  vol.  25,  no.  9,  p.  824. 

40  Loc.  cit. 

41  Cited  from  Sullivan,  loc.  cit.,  p.  12. 

42  Cited  from  Sullivan,  loc.  cit.,  p.  13. 

«  Landw.  Vers.  Stat.,  vol.  2,  p.  113,  1860. 

44  Loc.  cit. 

45  Oregon  Agrie.  Exper.  Sta.,  Bull.  112,  1912. 

4«  New  Hampshire  A.gric.  Exper.  Sta.,  Bull.  170,  1914. 

47  Loc.  cit.  ■ 

4*  U.  8.  Dept.  Agric,  Bur.  of  Soils,  Bull.  82. 

4»  U.  S.  Dept.  Agric.,  Bur.  of  Soils,  Bull.  52,  1908. 

•r>o  Abstract   in    Journ.   Chem.    Soc.   London,    vol.    102,   no.    597,   p.    677, 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  329 

which  the  same  strength  of  different  salt  solutions  operates  to 
clarify  suspensions  from  different  soils.  Moreover,  the  addition  of 
these  salts  seems  to  bring  about  a  decided  increase  in  the  colloidal 
content  of  the  soil,  which  is  obviously  manifested  when  the 
soluble  salts  are  removed  by  distilled  water.  On  the  other  hand, 
the  introduction  of  calcium  salts  to  a  soil  does  not  apparently 
bring  about  the  production  of  a  colloidal  complex,  although  some 
interchange  of  ions  occurs.  In  fact,  the  addition  of  CaCl2  fol- 
lowed with  washing  seems  to  have  the  opposite  effect  on  the  Davis 
clay-loam  soil.  For  these  reasons  it  seems  evident  that  the  in- 
soluble as  well  as  the  soluble  products  formed  by  the  interaction 
of  salts  on  soils  must  be  considered  as  important  factors  in  such 
practices  as  prescribe  the  use  of  soluble  salts  on  soils. 

It  is  apparent  that  at  least  the  Na,  K  and  NH4  ions  form  a 
colloidal  substance  upon  their  introduction  into  the  silicate  com- 
plexes of  the  Davis  soil.  The  Ca-ion,  and  probably  others,  form, 
on  the  contrary,  non-colloidal  substances  when  introduced  into 
the  complex  silicates  of  the  Davis  soil.  It  is  also  made  clear 
that  the  acid  ion  is  of  little  importance  in  the  phenomena  follow- 
ing the  washing  out  of  salts  from  the  soil,  by  the  fact  that  NaN03, 
NaCl  and  Na2S04  all  operate  to  produce  approximately  the  same 
results. 

Some  General  Observations  on  Other  Peculiar  Appearances 

Accompanying  the  Washing  Out  of  Certain 

Salts  from  Soils 

Stewart51  in  a  recent  paper  attributes  the  color  of  the  nitre 
spots  to  the  action  of  sodium  or  potassium  nitrates  on  the  organic 
matter  of  the  soil.  Bearing  somewhat  upon  this  subject,  we  have 
noted  that  the  addition  of  NaCl  or  Na2S04  to  a  soil  materially 
increases  the  organic  matter  in  the  supernatant  solution  if  the 
depth  of  color  of  such  a  solution  can  be  relied  upon  as  an  index 
of  the  quantity  of  organic  matter  contained  therein.  But  the 
most  striking  results  in  this  connection  appear  when  these  neutral 
salts  are  removed  from  the  soil  by  washing.  The  soil  itself  as- 
sumes the  typical  gray  color  of  alkali  soils  in  the  field,  and  the 


si  Journ.  Amer.  Soc.  Agron.,  vol.  6,  no.  6,  p.  247,  1914. 


330         University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

filtrate  takes  on  a  rich,  dark  brown  color,  not  unlike  the  usual 
NH4OH  humus  extract.  Frequently  the  soil  when  dry  is  covered 
with  a  thin  layer  of  hard,  black,  organic  matter.  Indeed  the  re- 
semblance between  the  NaCl  +  H20  soil,  the  water  in  contact 
with  it,  or  its  percolate,  and  the  natural  alkali  soils  and  the  water 
bathing  their  particles,  is  so  striking  as  to  deceive  even  those 
experienced  in  the  handling  of  ' '  black  alkali ' '  soils. 

The  increased  solubility  of  the  organic  matter  in  the  salt- 
treated,  water-Avashed  soils,  as  indicated  by  the  increased  depth 
of  the  brown  color,  cannot  be  due  to  the  presence  of  the  NaCl 
as  a  chemical  entity,  for  the  color  does  not  appear  until  after 
some  of  the  salt  has  been  removed  from  the  soil  by  washing.  There 
can  be  no  doubt  that  the  NaN03  by  means  of  an  interchange  of 
ions  with  the  organic  salts  of  calcium  or  magnesium  does  affect  a 
greater  solubility  of  organic  matter,  but  this  solubility  may  be 
greatly  increased  if  the  added  salt  is  washed  from  the  soil.  This 
fact  may  be  of  assistance  in  accounting  for  the  color  of  the  nitre 
spots. 

In  agreement  with  Van  Bemmelen52  and  Warington,53  we  have 
also  noted  the  appearance  of  fluffy,  flocculent  colloids  passing 
through  the  filter  paper,  when  the  added  salt  is  practically 
washed  from  the  soil.  These  colloids  coagulate  when  in  contact 
with  the  filtrate  containing  the  soluble  salts  from  the  soil. 

One  other  point  which  has  not  received  prior  attention,  but 
which  seems  of  sufficient  importance  to  be  mentioned  at  this 
time,  is  the  fact  that  all  of  the  salt  need  not  be  washed  from  the 
soil  to  produce  the  effects  noted.  In  another  series  of  experiments, 
which  will  be  reported  in  detail  later,  3200  cc.  of  a  1.5  per  cent 
solution  of  NaCl  (which  was  intended  to  represent  the  strength 
of  the  soil  solution  when  0.3  per  cent  of  NaCl  is  added  to  the  soil 
under  optimum  water  conditions)  was  passed  through  1600  grams 
of  Davis  soil.  The  soil  was  affected  to  a  greater  extent  than  a 
soil  receiving  a  similar  quantity  of  NaCl,  namely  4.8  grams,  or 
than  a  third  soil  receiving  a  similar  quantity  of  NaCl,  which  in 
addition  was  leached  with  3200  cc.  of  water.  The  injury  to  the 
first  soil  was  greater  than  to  the  other  soils  despite  the  fact  that 


52  hoc.  cit. 

53  Loc.  cit. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  331 

a  small  quantity  of  salt  remained  in  contact  with  the  soil.  These 
observations  lend  further  confirmation  to  the  fact  previously  ob- 
served, that  a  second  addition  of  NaCl  to  a  NaCl  +  H20  soil 
does  not  cause  the  reversion  of  the  soil  to  its  original  condition. 

General  Discussion  op  the  Effects  Noted  and  Their 

Application  to  Soil  Studies  and  the 

Management  of  Soils 

In  the  discussion  on  the  possible  relation  of  the  calcium  and 
magnesium  content  of  the  percolate  to  the  diffused  condition  of 
salt-treated,  water-washed  soils,  attention  has  already  been 
called  to  the  fact  that  the  phenomena,  first  observed  in  case  of 
the  cylinders  containing  Davis  soil,  also  appeared  in  three  other 
soils  of  widely  different  types.  Evidently  the  effects  observed 
when  added  salts  are  washed  from  soils  by  distilled  water,  are 
not  peculiar  to  any  particular  type  of  soil,  but  are  more  or  less 
general  in  their  application.  Some  soils,  as  those  which  do  not 
offer  replaceable  calcium  or  magnesium  to  exchange  for  sodium 
or  other  ions  of  salt  solutions,  would  probably  react  to  a  much 
less  extent  than  those  soils  which  do  react  with  salt  solutions. 
The  degree  to  which  the  soil  is  affected  by  the  salt-and-water 
treatments  is  apparently  dependent  upon  the  amount  of  exchange 
of  bases,  or  the  direct  addition  of  bases  which  occurs.  This,  of 
course,  varies  markedly  with  different  soil  types  and  is  probably 
closely  associated  with  complex  silicates  of  which  mention  has 
already  been  made.  This  conception  conforms,  in  the  main,  with 
the  ideas  brought  out  by  Knop,54  Van  Bemmelen,55  and  AVaring- 
ton,56  with  respect  to  the  absorption  of  salts  by  soils.  Moreover, 
Kossovich57  has  noted  that  NaCl  exercises  a  more  pronounced 
effect  on  capillary  rise  in  clay  soils  than  in  sandy  soils. 

There  can  be  but  little  doubt  that  the  effects  of  salts  on  the 
physical  and  chemical  properties  of  soils  has  a  wide  range  of 
application  to  alkali  soils  and  their  management.     Moreover,  the 


54  Cited  from  U.  S.  Dept.  Agric,  Bur.  of  Soils,  Bull.  52,  p.  19. 
ss  Loc.  cit. 

56  Loc.  cit. 

57  Loc.  cit. 


332         University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

peculiar  phase  of  these  effects  under  consideration  would  seem  to 
have  particular  significance  in  that  connection.  First  of  all, 
these  soils  contain,  as  a  general  rule,  sufficiently  large  quantities 
of  salts  to  be  commensurate  with  those  used  in  the  experiments 
reported  above.  Secondly,  the  natural  rainfall,  irrigation  prac- 
tices, and  drainage  operations  often  wash  the  salts  out  of  the 
top  layers  of  soil,  so  that  this  soil  would  be  exposed  to  the  con- 
ditions likely  to  produce  the  inferior  physical  qualities  attendant 
upon  deflocculation. 

During  the  late  winter  and  early  spring  months  the  writer 
had  occasion  to  observe  the  standing  water  in  the  depressions  of 
the  alkali  lands  near  Fresno,  California.  To  all  appearances  the 
underdrainage  of  these  low  areas  would  be  practically  impossible, 
owing  to  the  imperviousness  of  the  soil,  which  upon  examination 
reveals  all  the  characteristics  of  the  diffused  salt-treated,  water- 
washed  soils.  Besides,  the  gray  appearance  of  the  soil  when  dry, 
and  the  striking  resemblance  of  the  supernatant  liquid  to  that 
above  the  soils  in  the  cylinders,  would  certainly  lead  one  to  be- 
lieve that  even  under  natural  conditions  the  washing  out  from 
and  the  dilution  of  the  salts  in  alkali  soils  has  much  in  common 
with  the  artificial  production  of  similar  conditions.  Heretofore, 
the  depressions  and  the  remarkable  imperviousness  of  their  soils 
have  been  attributed  to  the  presence  of  Na2C03. 

It  would  seem  that  the  deflocculation  effects  exhibited  by  soils 
when  added  salts  are  washed  from  them  would  have  particular 
bearing  upon  the  reclamation  of  alkali  soils  by  underdrainage. 
Yet  the  possible  application  of  this  feature  to  alkali  reclamation 
seems  to  have  been  omitted  from  the  literature  dealing  with  this 
subject.58  Cameron  and  Patten59  observed  somewhat  similar 
lowering  of  the  rate  of  percolation,  followed,  however,  by  an 
increase  later  as  the  washing  out  of  the  salts  progressed.  Hare,60 
in  a  recent  paper  describing  tank  experiments  dealing  with  the 
effects  of  alkali  salts  on  soils  and  crops,  does  not  note  any  pos- 
sible effect  of  the  added  salts  on  percolation  through  the  soils 
receiving  them,  but  does  comment  on  the  observation  that  Na2S04 

58  Hilgard,  Soils,  1911,  chap.  22,  and  U.  S.  Dept.  Agric,  Bur.  of  Soils, 
Bull.  35,  1906. 

69  Journ.  Amer.  Chem.  Soc,  vol.  28,  p.  1639,  1906. 
oo  New  Mexico  Agric.  Exper.  Sta.,  Bull.  88,  1913. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  333 

was  more  difficult  to  leach  from  the  soil  than  Na2C03  or  NaCl. 
Specific  information  on  the  physical  condition  of  the  drained 
alkali  soils  of  the  various  drainage  experiments  is  lacking.  Even 
the  recorded  observations  of  a  general  nature  are  indefinite  and 
discordant.  Thus  at  Salt  Lake,61  Tempe,62  and  North  Yakima,63 
the  effect  of  drainage  has  not  appeared  to  have  benefitted  the 
physical  condition  of  the  soil,  while  at  Fresno,64,  Billings,05  and 
elsewhere,  the  drained  soil  appeared  to  be  superior  with  respect 
to  physical  condition  than  the  undrained  soil.  Owing  to  the  in- 
adequacy of  these  reports  in  that  no  definite  measurements  of 
alteration  in  the  physical  condition  of  the  soil  are  given,  they 
cannot  be  accepted  as  a  final  expression  of  the  effects  of  drainage 
of  alkali  soils. 

The  behavior  of  the  Davis  soil  in  the  cylinders  and  the  general 
trend  of  the  laboratory  experiments  seem  to  the  writer  convincing 
arguments  that  the  drainage  of  these  cylinder  soils  in  their 
present  condition  would  be  practically,  perhaps  absolutely,  im- 
possible. Underdrainage,  supplemented  with  powerful  flocculat- 
ing agents,  might  serve  as  a  feasible  plan  whereby  the  excess  salt 
could  be  removed  from  such  soils. 

That  natural  alkali  soils  are  not  strictly  comparable  with  the 
cylinder  soils  to  which  single  salts  have  been  added  is  patent, 
and  this  may  account,  in  a  measure,  for  the  general  discrepancy 
between  the  behavior  of  certain  natural  alkali  soils  and  that  of 
alkali  soils  made  artificially  by  the  addition  of  salts.  The  wash- 
ing out  of  salt  mixtures,  as  in  the  case  of  natural  alkali  soils,  may 
have  an  entirely  different  effect  than  the  washing  out  of  a  single 
salt.  It  has,  however,  been  shown  in  this  laboratory  that  the 
washing  out  of  certain  mixtures  of  salts  from  the  Davis  soil  has 
resulted  in  the  same  way  as  washing  out  single  sodium  salts.  On 
the  other  hand,  the  time  for  the  reaction  of  the  salt  in  the  soil 


6iDorsey,  C.  W.,  U.  S.  Dept.  Agric.  Bur.  of  Soils,  Bull.  43,  p.  16, 
1907,  and  Bull.  35,  p.  181,  1907. 

esDorsey,  C.  W.,  U.  S.  Dept.  Agric,  Bur.  of  Soils,  Bull.  35,  p.  190, 
1907. 

«s  Loc.  cit.,  p.  189. 

64Mackie,  W.  W.,  U.  S.  Dept.  Agric,  Bur.  of  Soils,  Bull.  42,  p.  43, 
1907. 

65Dorsey,  C.  W.,  U.  S.  Dept.  Agric,  Bur.  of  Soils,  Bull.  44,  p.  18, 
1902. 


334        University  of  California  Publications  in  Agricultural  Sciences   [Vol.  1 

being  comparatively  unlimited  in  case  of  the  natural  soils,  it  may 
considerably  alter  the  end-points  and  end-products  and  thus 
introduce  a  new  factor.  The  constant  up-and-down  movement 
of  the  soluble  salts  in  the  soil,  the  alternate  drying  and  wetting 
of  the  soil,  and  the  effects  of  thermal  changes  on  the  soil,  may 
partially  obliterate  the  true  effects  of  washing  certain  salts  from 
soils.  In  addition,  the  relation  of  calcium,  magnesium  and  other 
bases  to  the  sodium  may  be  modified  by  the  conditions  just  men- 
tioned, so  that  different  equilibria  are  established.  Furthermore, 
the  nature  of  the  soil,  especially  with  respect  to  the  original  con- 
tent of  colloidal  substances  and  hydrated  silicate  complexes,  must 
be  taken  into  account.  Thus  the  effect  of  draining  salts  from 
sandy  soils  free  of  colloids  may  be  so  small  as  to  pass  unrecog- 
nized, while  similar  drainage  from  heavier  types  of  soils  would 
produce  marked  effects.  The  colloidal  content,  too,  and  the  state 
of  diffusion  thereof,  in  our  drained  alkali  lands,  may  be  a  direct 
result  of  the  first  natural  introduction  of  the  salts  into  and  their 
subsequent  removal  from  the  original  soil,  the  exact  physical 
condition  of  which  may  be  only  surmised.  Hence  we  have  no 
means  for  securing  evidence  as  to  the  exact  salt  effects  under 
natural  conditions. 

As  suggested  by  Mayer,66  the  physical  effects  resulting  from 
washing  sea  salts  from  the  soil  may  be  as  injurious  to  the  growth 
of  plants  as  the  direct  toxicity  of  the  salt  itself.  Our  experience 
with  the  cylinders  serves  to  confirm  this  idea,  for  olespite  the 
fact  that  the  top  foot  of  soil  is  almost  free  from  salts,  it  seems 
impossible  to  secure  a  satisfactory  growth  of  plants.  A  pot 
experiment,  to  be  reported  upon  later,  also  gives  substantial 
proof  that  the  deflocculated  soil,  comparatively  free  from  salt, 
offers  a  far  less  congenial  home  for  barley  plants,  at  least  during 
the  early  stages  of  growth,  than  the  same  soil  containing  as  high 
as  0.3  per  cent  of  NaCl. 

The  inability  of  the  plants  to  make  a  satisfactory  growth  in 
the  highly  deflocculated  soils  appears,  from  a  cursory  considera- 
tion of  the  conditions,  to  be  due  to  the  lack  of  available  moisture. 
Although  the  deflocculated  soils  may  seem  to  be  moist,  yet  the 
quantity   of   water  which  the   plants  have   at   their  disposal  is 


66  hoc.   Cit. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  335 

probably  insufficient  to  promote  normal  growth.  At  least  this 
condition  is  suggested  by  the  moisture  equivalents  of  the  defloc- 
culated  NaCl  +  H20  soil  as  determined  with  the  centrifugal 
machine  developed  by  Briggs.  In  addition  to  the  low  availability 
of  the  moisture  in  such  soils  as  an  inhibiting  factor,  the  rate  of 
movement  of  water  through  such  soils  must  also  be  considered 
in  its  relation  to  the  growth  of  plants.  From  all  appearances,  it 
seems  justifiable  to  predict  that  the  movement  of  water  through 
the  highly  diffused  soils  is  so  slow  as  to  fail  to  resupply  the  area 
occupied  by  the  roots  from  the  more  moist  soil  layers  lying 
adjacent  to  the  root  area. 

The  observed  effects  of  washing  salts  from  soils  may  also  have 
some  bearing  upon  fertilizer  practices  and  the  results  on  crop 
plants  secured  therefrom.  The  salts  used  as  fertilizers  undoubt- 
edly effect  certain  modifications  of  the  physical  condition  of 
soils.  It  is  also  true  that  the  washing  out  from  the  soil  of  at 
least  some  of  these  salts  brings  a  far  greater  change  in  the 
physical  properties  of  the  soil  than  that  accompanying  the  ap- 
plication of  the  salts.  Probably  no  instance  writh  respect  to  this 
feature,  as  a  phase  of  soil  management,  is  so  patent  as  that  con- 
cerning the  use  of  NaN03.  Hall67  comments  upon  the  inadvis- 
ability  of  applying  this  material  under  certain  conditions  be- 
cause of  the  deflocculating  effect  of  the  alkalinity  due  to  residual 
sodium  carbonate.  Warington08  also  notes  the  deflocculating 
effect  of  NaN03  and  refers  to  it  as  being  particularly  noticeable 
after  heavy  rains.  More  recently  McGeorge69  has  observed  a 
marked  retardation  of  percolation  through  Hawaiian  soils  receiv- 
ing applications  of  NaN03,  but  attributes  this  effect  to  some 
reaction  between  the  added  salt  and  the  organic  matter  of  the 
soil.  Undoubtedly  the  application  of  NaN03  to  soils  under  cer- 
tain circumstances  has  resulted  in  a  deterioration  of  the  physical 
condition  of  the  soil,  although  the  NaN03,  as  a  salt,  is  in  itself 
a  flocculating  agent. 

The  writer  has  produced  marked  deflocculation  in  the  Davis 
soil  by  applying  NaN03  and  subsequently  washing  the  soluble 


67  The  Soil,  p.  252,  1910. 

es  Loc.  cit. 

eo  Hawaiian  Agric.  Exper.  Sta,  Bull.  35,  1914. 


336         University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

salts  from  the  soil  with  water.  The  use  of  the  N03  radical  by 
plants  or  bacteria,  thereby  leaving  the  sodium,  could  not  have 
occurred  to  any  extent  in  this  case,  for  the  whole  process  re- 
quired no  longer  than  two  hours,  and  was  carried  out  in  a  filter. 
The  filtrate  at  no  period  in  the  washing  process  showed  sufficient 
alkalinity  to  account  for  the  deflocculation.  Hence  the  former 
conception  that  residual  Na2C03  causes  the  deflocculation  seems 
untenable,  and  some  such  hypothesis  as  has  been  advanced  in 
this  paper  must  be  adopted  to  explain  the  unfavorable  physical 
condition  frequently  existing  in  soils  receiving  applications  of 
NaN03. 

With  respect  to  fertilizer  salts  in  general,  Hall70  calls  attention 
to  the  deflocculation  following  the  use  of  neutral  salts  on  soils, 
but  believes  the  effect  is  due  to  alkalinity  arising  from  the  ab- 
sorbed base.  Hessler71  has  noted  the  increase  in  coherence  of  the 
soil  particles  when  NaCl,  NaN03  and  kainite  have  been  applied 
to  soils.  Hoffman,72  however,  could  not  detect  any  difference  in 
the  interior  surface  of  soils  due  to  fertilizer  applications  of  the 
usual  magnitude.  It  is  of  interest  to  note  that  no  attempt  is 
made  to  correlate  the  inferior  physical  condition  of  salt-treated 
soils  with  the  process  of  leaching  the  salts  from  them. 

However,  potassium  and  ammonium  salts  are  effective  in  the 
same  direction  as  sodium  salts  when  washed  from  the  soil,  al- 
though they  are  generally  considered  flocculating  agents  when 
in  contact  with  certain  colloidal  particles.  Hence,  to  be  fully 
comprehensive  and  expressive  of  the  whole  truth,  studies  on  fer- 
tilizer effects  should  involve  not  only  the  conditions  under  which 
the  salt  or  salts  are  present,  but  also  those  conditions  which  not 
infrequently  arise  in  nature,  whereby  the  soluble  salts  are  re- 
moved from  the  soil  by  processes  analogous  to  washing  the  soil 
with  water. 

The  nature  of  the  clay  colloids  and  the  cause  of  the  relatively 
high  degree  of  deflocculation  which  they  assume  when  suspended 
in  water  have  long  been  subjects  of  much  conjecture  and  much 


70  7,0c.  cit. 

7i  Cited  from  Exper.  Sta.  Rec,  vol.  31,  no.  2,  p.  123,  1914. 

72  Landw.  Vers.  Stat.,  vol.  85,  nos.  1-2,  p.  123,  1914. 


1916]  Sharp :  Soluble  Salts  and  Soil  Colloids  337 

debate.  Hilgard73  has  consistently  maintained  that  the  power 
of  such  colloids  to  remain  in  a  stabilized  condition  is  not  to  be 
attributed  solely  to  the  fineness  of  division  of  such  particles,  but 
that  other  factors  may  be  responsible  for  that  condition.  In 
agreement  therewith,  our  experience,  which  has  been  presented 
in  this  communication,  has  led  us  to  believe  that  the  chemical 
nature  of  the  body  itself  and  that  of  the  medium,  determine  in  a 
large  measure  the  condition  in  which  the  colloid  may  exist. 

The  extent  to  which  the  factor  considered  in  this  paper  may 
be  applicable  to  agricultural  practice  can  be  better  surmised  than 
asserted  at  the  present  writing,  but  it  seems  highly  possible  that 
the  modifications  of  the  physical  condition  of  the  soil,  due  to 
washing  out  the  soluble  salts,  under  circumstances  involving 
fertilizer  applications  or  natural  alkali  soils,  will  be  reflected  in 
the  inferior  tilling  qualities  of  the  soil,  in  the  increased  resistance 
offered  by  such  soils  to  root  penetration,  in  the  lack  of  air  space 
and  air  movements,  in  the  deflocculated  soil,  and  in  the  moisture 
and  temperature  relations  of  such  diffused  soils.  The  movement 
of  moisture  in  soils  by  surface  tension  and  osmotic  pressure  or 
under  gravitational  attraction,  appears  to  be  particularly  de- 
pendent upon  the  degree  of  deflocculation  of  the  soil  colloids. 

Besides  affecting  the  physical  condition  of  the  soil,  the  leach- 
ing out  of  soluble  neutral  salts  from  soils  is,  as  has  been  previously 
shown,  frequently  accompanied  by  notable  quantities  of  calcium 
and  magnesium  in  the  percolate.  Thereby  the  soil  sustains  a  con- 
siderable loss  of  calcium  and  magnesium,  which  may  in  the  course 
of  time  be  of  sufficient  magnitude  actually  to  deplete  the  available 
supply  of  these  plant-food  elements  in  the  soil.  The  bacterial 
flora  and  bacterial  activity  of  soils  subjected  to  the  treatments 
outlined  above  are  liable  to  be  considerably  modified  and  to  all 
appearances  in  a  harmful  direction.  Thus  all  the  factors  of  soil 
fertility  are  likely  to  be  measureably  affected  through  the  pro- 
cess of  washing  salts  from  soils ;  consequently  the  crop-producing 
power  of  the  salt-treated,  water-washed  soil  is  apt  to  be  con- 
siderablv  modified. 


Soils,  chap.  VI. 


338         University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

Summary 

1.  The  Davis  claj^-loam  soil  to  which  surface  applications  of 
solutions  of  NaCI,  Na2S04  and  Na2C03  had  been  made  became 
very  impervious  to  water,  difficult  to  cultivate,  and  manifested 
the  characteristics  of  a  high  degree  of  diffusion,  although  these 
salts  have  been  shown  to  exercise  flocculating  powers  on  sus- 
pensions of  this  soil. 

2.  The  salt-treated  soils  referred  to  were  in  cylinders  exposed 
to  natural  conditions. 

3.  Examination  of  the  soils  showed  that  the  salts  had  moved 
downward  into  the  lower  layers  of  soil  and  that  only  the  surface 
soil  had  been  affected  in  the  direction  described. 

4.  The  deflocculated  condition  resulting  from  adding  certain 
salts  to  and  subsequently  washing  them  from  soils  can  be  repro- 
duced in  the  laboratory. 

5.  The  deflocculation  of  soils  treated  in  the  manner  described 
above  is  intimately  associated  with  the  leaching  of  the  NaCI  and 
Na2S04  down  into  the  lower  layers  of  soil  by  water.  In  the  case 
of  Na2C03  the  leaching  process  is  not  so  essential  for  the  diffusion 
of  the  soil  colloids. 

6.  The  addition  of  NaCI,  Na2S04  and  Na2C03  to  the  Davis 
soil  when  followed  with  applications  of  water  was  particularly 
effective  in  diminishing  the  rate  of  percolation  through  the  soil 
so  treated. 

7.  NaCI  and  Na2S04  in  constant  contact  with  the  Davis  soil 
increased  the  rate  of  percolation,  except  when  a  comparatively 
dilute  solution  of  NaCI  was  slowly  passed  through  the  soil  for  a 
considerable  period  of  time. 

8.  The  Davis  soil  treated  with  NaCI,  NaOH,  Na2C03  and  other 
salts,  followed  by  leaching  with  water,  yields  a  suspension  in 
water  containing  approximately  ten  times  as  much  solid  matter 
as  the  same  soil  washed  with  water  only.  A  real  diffusion  in  such 
salt-treated  soils  seems  evident. 

9.  The  soil  once  diffused  by  washing  out  added  NaCI  requires 
considerably  more  salt  to  completely  flocculate  it,  than  does  the 
water- washed  soil.  Likewise  the  injured  physical  condition  of 
such  soils  is  not  readily  repaired  by  a  second  addition  of  NaCI. 


1916]  Sharp:  Soluble  Salts  and  Soil  Colloids  :;:;!» 

10.  The  portion  of  the  organic  matter  of  the  soil  known  as 
humus  has  little  or  no  connection  with  the  appearance  of  dif- 
fusion in  salt-treated,  water-washed  soils. 

11.  The  diffusion  in  soils  treated  as  described  above  seems  to 
be  closely  associated  with  the  direct  addition  of  sodium  to,  or 
with  the  absorption  of  sodium  by  the  soil,  thereby  producing  a 
new  silicate  complex  of  a  colloidal  character  in  the  soil. 

12.  This  silicate  complex  is  formed  simultaneously  with  the 
interchange  of  ions  occurring  between  the  salt  and  the  soil. 

13.  The  washing  process  serves,  in  the  case  of  neutral  salts. 
to  remove  flocculating  agents. 

14.  The  loss  of  calcium  and  magnesium  from  the  soil  bears 
little  or  no  relation  to  the  flocculation  appearing  in  salt-treated, 
water-washed  soils  except  in  so  far  as  it  may  be  a  measure  of  the 
absorbed  sodium. 

15.  The  presence  of  the  OH-ion  does  not  seem  to  be  an  essen- 
tial factor  in  the  diffusion  of  salt-treated,  water-washed  soils. 

16.  Na2C03  and  NaOH  produce  markedly  different  effects  on 
suspensions  of  the  Davis  soil. 

17.  The  acid  ion  of  the  salt  is  not  an  important  factor  in  the 
deflocculation  phenomena  following  the  washing  out  of  salts 
from  soils. 

18.  Sodium,  potassium,  and  ammonium  seem  to  produce  the 
colloidal  silicate  complex  when  salts  of  these  metals  are  applied  to 
soils,  while  calcium  does  not. 

19.  Dilute  solutions  of  acids  and  salts  possess  flocculating 
powers  on  suspensions  of  the  Davis  soil. 

20.  It  is  not  essential  in  every  case  to  wash  all  of  the  salt 
out  in  order  to  bring  about  diffusion. 

21.  The  facts  presented  are  discussed  in  their  relation  to  the 
reclamation  and  management  of  alkali  lands,  and  in  their  appli- 
cation to  the  use  of  soluble  salts  as  fertilizers. 

The  writer  desires  to  express  his  thanks  to  Professor  Charles 
B.  Lipman  for  many  valuable  suggestions  and  for  his  critical 
reading  of  the  manuscript,  and  to  L.  E.  Bailey  for  his  timely 
assistance  in  the  analytical  work. 

Transmitted  November  16,  1915. 


